Improving Functional Performance of TKA

Figure 1: Diagram demonstrating the modification of the J curve of the femoral component of some “high-flexion” TKA designs.

Enhancing range of motion (ROM) and muscle function are crucial to improving functional performance of TKA.

Replication of the normal knee kinematic pattern is critical to maximize knee flexion and physical function.

In vivo fluoroscopic studies of normal knee kinematics demonstrate that posterior femoral roll-back of the lateral femoral condyle, averaging 14.1 mm, routinely occurs during deep flexion.

Deep flexion is also associated with substantial axial rotation, averaging 16.8°.²

These kinematic differences from the normal knee likely account, at least in part, for the reduction in knee flexion and reduced motor function typically observed following TKA when compared with the normal knee.

Future designs of TKA should focus on providing reproducible roll-back and increased axial rotation.

Recent design efforts to improve knee flexion have been incorporated into high-flexion TKA designs.

These high-flexion devices allow for posterior cruciate ligament substitution, which enhances posterior femoral roll-back, and bearing mobility, which permits increased amounts of axial rotation without creating excessive rotational polyethylene stresses.

Many of these newer designs have also reduced the radius of curvature (“J” curve) of the posterior femoral condyles, both to increase the posterior femoral translation distance and reduce polyethylene stresses in deep flexion

Cruciate-retaining versus Cruciate-sacrifcing TKA

Very few surgeons attempted to retain both cruciate ligaments; it was considered too difficult by most surgeons, despite reports of good clinical results.²⁴ Retaining the posterior cruciate ligament (PCL) was preferred in young and active patients, because of its important mechanical and proprioceptive qualities.

According to Mueller, it was unclear whether the PCL (the lateral collateral ligament of the medial compartment of the knee and an important stabilizing force against varus-valgus rotations) could also help provide stability in the anteroposterior direction and in femoral roll-back during flexion of the knee in the absence of the anterior cruciate ligament.

Some PCL-retaining knees proved to be unstable in the anteroposterior direction, sometimes even demonstrating a negative roll-back movement, with negative consequences for the meniscal bearings, including breakage, dislocation, and wear.

Mobile-bearing knee replacement system

In the 1970s and 1980s, polyethylene wear was not widely recognized as a major cause of aseptic loosening of total knee components.

The concept was not well appreciated by orthopedic surgeons, despite the fact that it was demonstrated in laboratory settings and prostheses-retrieval studies.

Many designers compromised to produce more conformity between components, while still allowing varus-valgus rotation and some axial rotation. This design concept remains the basis for many knee replacement systems.

Mobile-bearing knee replacement systems were designed to prevent mechanical loosening and wear, the two primary shortcomings of knee replacement systems.

Studies from the 1960s and 1970s demonstrated good results with conventional fixed-bearing total knee arthroplasty (TKA) systems at 10- to 15-years’ follow-up.

However, patients at that time were older and less active than patients are today, and thus there was less demand on implants.

Indications for TKA are changing rapidly; today’s patients are more active, and therefore require more durable knee replacement systems, and patients are seeking TKA for knees damaged by excessive weight, accidents, and sports injuries.

It became clear to early designers of knee prostheses that TKA should entail more than simply replacing cartilage with metal and polyethylene and providing stability through the intrinsic constraint of the components.

Clinical follow-up showed that achieving stability through intrinsic constraint was detrimental to fixation and that unnecessary prosthetic constraints should be avoided to minimize the transmission of forces to the bone-prosthesis interface.

Free anatomic motion between components was recommended not only to improve function, but to prevent mechanical loosening of components.

These changes had consequences, however; in knee prostheses with fixed bearings, minimal constraint against displacement resulted in small contact areas and high contact stresses.

Though minimal torque was transmitted to the fixation interfaces and mechanical loosening was reduced, there was an increased risk of polyethylene articulation damage.

Mobile-bearing knees were found to have a significantly lower incidence of delamination than fixed-bearing knees, despite these bearings all having been sterilized with gamma irradiation in an air environment and then stored in air.

It had become clear from earlier research that gamma radiation and air storage resulted in degradative oxidation of the polyethylene.

The superior results among mobile-bearing knees in the study, however, suggested that a design factor, namely congruity, which affords a large contact area to reduce contact stress, accounted for this apparent discrepancy.

The importance of reducing wear by increasing the contact areas has been confirmed. Recently, McEwen et al demonstrated that LCS mobile-bearing rotating-platform knee designs result in a significantly lower mean volumetric wear rate of polyethylene than fixed-bearing knee designs, especially when subjected to high internal-external rotational kinematic inputs.

The mobility characteristics and gait patterns of patients with mobile bearings have also been studied extensively, confirming the superiority of mobile-bearing TKA over fixed-bearing TKA in long-term follow-up.

Mobile-bearing systems were designed to prevent mechanical loosening and wear, the two primary complications of knee replacement. Today, after more than 25 years in clinical use, and with overwhelming evidence from clinical experience, laboratory experiments and retrieval analysis, the mobile-bearing concept underlying rotating-platform knee systems has proven to be reliable. The LCS rotating-platform knee, unchanged in almost 30 years, remains a relevant and important design concept.

It is important to note the important design features of mobile-bearing knees. Polyethylene components need to be mobile in a manner that movement is restricted by soft tissues rather than by intrinsic constraint, and bearings must provide sufficient stability to compensate for the absence of the cruciate ligaments. Also, femorotibial contact areas should be large to prevent wear, especially considering condylar lift-off during gait. Finally, movement proximally and distally of the polyethylene bearing should be unidirectional rather than controlled by metal stops, also to prevent wear.

An additional advantage of the self-aligning feature of rotating-platform TKA systems is the potential facilitation of central patellar tracking.

In a fixed-bearing TKA, if substantial internal rotation of the tibial component relative to the femoral component is present, the tibial tubercle is lateralized, enhancing the risk of patellar subluxation.

A rotating-platform design, because of bearing rotation, permits greater self-correction of component rotational malalignment and allows better centralization of the extensor mechanism.

Summary of important points.

The original patent for mobile-bearing rotating-platform knee systems owned by DePuy expired in 1997, allowing manufacturers to develop their own mobile-bearing prosthesis.

Although most rotating-platform knees look alike, there are major differences in design.

In some rotating-platform designs, the femorotibial contact area is very large, and in other designs, the contact area is rather small.

Some designs incorporate unidirectional movement at the distal surface between the polyethylene bearing and tibial tray, whereas others utilize multidirectional gliding at the distal surface.

There also are significant differences in how bearing movement is controlled.

Some mobile-bearing knee systems incorporate a certain amount of constraint.

In others, bearing movement is controlled by metal cylinders, slots, or stops that may be effective in controlling bearing movement, but may produce suboptimal kinematics and stress on the polyethylene leading to damage and wear.

Because of these design differences, long-term follow-up studies should be undertaken to determine variations in results.

Ref:

McEwen HM, Goldsmith AAJ, Auger DD, et al. Wear of fixed bearing and rotating platform mobile bearing knees subjected to high internal and external tibial rotation kinematics. J Mater Sci Mater Med. 2001; 12:1049-1052.

Question of the day

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Figure 1

Figure 2

A 56-year-old man presents for treatment of chronic ankle pain. He has noted long-standing pain associated with activities since early adulthood. He does not have any other pertinent musculoskeletal history. Clinical and radiographic examinations reveal ankle arthritis. A probable cause for this arthritis and deformity is: (A) Recurrent ankle instability (B) Idiopathic osteoarthritis (C) Rheumatoid arthritis (D) Post traumatic arthritis (E) Anterior ankle impingement syndrome (A) Recurrent ankle instability (B) Idiopathic osteoarthritis (C) Rheumatoid arthritis (D) Post traumatic arthritis (E) Anterior ankle impingement syndrome

Explanation: The varus ankle deformity indicates either a chronic hindfoot varus and hindfoot cavus, or chronic recurrent instability of the ankle. If associated with rotatory instability, anterior impingement and eventual arthritis will occur.

Bibliography: Acevedo JI, Myerson MS. Reconstructive alternatives for ankle arthritis. Foot Ankle Clin. 1999; 4:409-430. Schon LS. Decision making in the athlete’s foot and ankle. In: Myerson MS, ed. Foot and Ankle Disorders. Philadelphia, Pa: WB Saunders; 2000.

Complications In TKR

Donald T. Reilly, MD. PhD

Introduction

At the recent State of the Art Update in Orthopaedics 2000 in Whistler, British Columbia, Lawrence G. Morawa, MD, moderated a group of presentations centered around the diagnosis and treatment of complications in total knee arthroplasty (TKA).

Diagnosing and Treating Infection
Although infection in total knee arthroplasty (TKA) is a relatively infrequent complication, it can be devastating in terms of morbidity and cost. Lester S. Borden, MD,[1] reviewed the diagnosis and treatment of infection in TKA. He began by stressing that this is a surgical disease. Long-term antibiotic depression is rarely indicated and is generally used only in patients for whom surgery is contraindicated.

Risk factors for knee infection include:
• multiple previous infections
• history of previous infection
• inflammatory arthritis (delayed infection)
• insulin dependent diabetes
• postthrombotic syndrome
• malnutrition.

Borden reviewed the importance of perioperative antibiotics. The institutional incidence of primary TKA infection should be around 1 %. Revision total knee replacement, however, carries at least a 2-fold increased risk for infection. In addition, late infections occur in approximately 2 per 1,000 TKAs annually.

Waldman and colleagues[2] retrospectively analyzed 290 patients with TKAs performed between 1982 and 1993 to define the risk for infection associated with dental surgery.

They identified 62 TKAs with late infections (occurring more than 6 months after procedure). Seven of these late infections were temporally and bacteriologically associated with dental procedures. Eight of 9 patients received no antibiotic prophylaxis. Fifty-six percent of the patients with late infections had positive risk factors, including diabetes and rheumatoid arthritis. These authors suggested prophylaxis for extensive dental work.

Diagnosing TKA infections is challenging, and prompt diagnosis and treatment are essential for a successful outcome. Windsor and colleagues[3] found that 96% of patients with infected TKAs presented with pain and 77 % had swelling. Only 27% had fever and drainage.

Treatment options for an infected TKA include:
• antibiotic suppression alone
• aggressive wound debridement, drainage, and antibiotic suppression therapy
• resection arthroplasty
• arthrodesis
• 2-stage reimplantation
• amputation.

The definitive diagnosis of infection is recovery of neutrophils by aspiration with greater than 30,000 leukocytes, 75% of which are polymorphonuclear. Five percent of infected TKAs in the Windsor study had negative cultures.
With an established infection, suppression is suggested only for patients in which surgery is not feasible. A low-virulence-organism, secure implant components, and well-tolerated oral antibiotics are required for cases in which suppression is chosen. Debridement with retention of the implant has a greater rate of success when there is meticulous synovectomy, copious irrigation, and parenteral antibiotics for 4 to 6 weeks in cases of acute infection.

According to Borden, management of infection with arthroscopy and multiple irrigations has yielded a lower rate of success. One-stage reimplantation, a more popular approach in Europe, may be possible for patients with acutely infected cementless TKAs and allows for debridement of the prosthesis-bone interface. Reimplantation usually requires antibiotic-impregnated cement. The gold standard for treatment of TKA infection remains the 2-stage reimplantation. This is especially successful in patients with chronically infected TKAs (ie, patients in whom symptoms persist for longer than 3 weeks.

Simmons and colleagues[4] performed a meta-analysis of 77 studies of 2-stage reimplantation and found an average success rate of 80%. This technique is more successful for cases of osteoarthritis with low-virulence bacteria and less successful for cases of rheumatoid arthritics and when high-virulence bacteria or multiple-organism infections are present. According to the Backe and colleagues,[5] a second 2-stage reimplantation following a failed 2-stage reimplantation has a success rate of approximately 80%.

There are few attractive surgical options for failed treatment of infected TKA. Arthrodesis should be considered when multiple surgical attempts fail to eradicate infection. Adequate bone stock, however, must be present for arthrodesis to be successful. Knee arthrodesis is challenging surgically and can be complicated by nonunion, malunion, or recurrent infection. A modular titanium intramedullary nail has been used in an attempt to reduce the incidence of nonunion and the rate of complications.

Waldman[6] reviewed the results of knee arthrodesis after infected TKA in 21 patients with a mean age of 64 years. Patients were followed for a mean of 2.4 years, and the mean number of previous operations was 4. Solid arthrodesis was achieved in 20 of 21 patients at approximately 6 months by using an intramedullary nail.

Borden discussed his personal approach to 2-stage reimplantation. His technique includes meticulous debridement with preservation of all noninvolved bone, preservation of collateral ligaments with resection of the posterior cruciate ligament, and the use of spacers (Prostalac). Prostalac remains interesting but controversial. He stressed the importance of skin closure. In the interval between removal and reimplantation, a patient should receive 4 to 6 weeks of intravenous antibiotics and no antibiotics for 1 to 2 weeks. An erythrocyte sedimentation rate and C-reactive protein test can be used to decide whether to reimplant. Borden emphasized the importance of antibiotics in cement used for reimplantation.

Looks Good, Feels Bad
Although the rate of dissatisfaction in patients with TKA is reported to be approximately less than 1%, evaluating a patient with pain or limited function is of utmost importance. James A. D’Antonio, MD,[7] reviewed the work-up of a patient with a painful or dysfunctional TKA.

D’Antonio presented a case of a 62-year-old active man who presented with pain. Plain radiographs and an examination appeared normal. However, slight rotation in several views other than ideal positioning showed loosening of an uncemented component. It is important to obtain fluoroscopic views if perfectly tangential radiographs of the prosthesis-bone interface are not available.

The second case was a 65-year-old man who reported that his knees were not supporting him. The examination revealed a very stable, well-aligned knee with no effusion. Radiographs showed no abnormalities. The patient had a history of alcoholism, which led to D’Antonio to the conclusion that the problem was with the patient not the arthroplasty. Evaluation of a patient who is unsatisfied with their

TKA should include:

• detailed history

• detailed physical examination, including chief complaints; pain; function; and neurovascular, psychosocial, and hip examinations

• radiographs and laboratory tests.

This work-up usually yields a diagnosis before surgery is necessary. D’Antonio stressed the importance of delaying surgery until the surgeon has reached a definitive diagnosis. Patients is key for surgeons encountering the small percentage of patients with TKA who are unhappy with unexplained pain or dysfunction.

Looks Bad, Feels Good
There are many failure mechanisms in TKA. These include:

• polyethylene wear

• instability

• aseptic Loosening

• extensor mechanism dysfunction

• unexplained pain

• infection.

George D. Markovich, MD,[8] examined the issue of “silent” osteolysis and the management of bone loss in TKA.

Femoral defects distally and posteriorly can be prevented with metal blocks on the femoral component to maintain the joint line.

Tibial wedges, half block, full block, and oblique full blocks are also useful.

Stems can be used enhance fixation when augments are used or bone quality is poor.

Markovich’s presented his experience with 50 revision TKAs with metal augmentation followed for a maximum of 10 years.

To date, none of his patients treated with this technique have had failure of fixation of the components.

Osteolysis due to polyethylene wear may be present in patients with few symptoms. As such, patients often do not present with symptoms until after extensive structural damage has already occurred.

Early treatment is central to the prevention of widespread bone loss.

There are few data to guide the decision to intervene.
Regardless of whether a patient has osteolysis, the surgeon should continue to focus on the goals of restoration of bone stock, reestablishment of the joint line, and recreation of stability in the revision setting.

Lonner and colleagues[9] evaluated a total of 102 revision TKAs to determine the prodromal symptoms and radiographic findings associated with failure. The most important indicator for failure was pain, occurring in 84% of patients at an average of 13 months. Radiographs underestimated the diagnosis of osteolysis to be 4%. Osteolysis was confirmed during surgery in 22% of patients. The authors recommended an annual questionnaire and weight-bearing radiographs to ensure adequate surveillance of TKA patients.

Radiographs often underestimate the extent of bone loss. This inadequacy has prompted the development of more exact techniques, such as dual-energy x-ray absorptiometry and microradiographic evaluation, into the clinical setting. These techniques, however, remain experimental. Because of the shortcomings of radiographs in diagnosing osteolysis, the surgeon needs to be prepared for more than is preoperatively visible.

Markovich briefly discussed pharmaceutical intervention to prevent osteolysis. Shanbaga and colleagues[10] evaluated oral bisphosphonate therapy in a canine total hip replacement model. The dogs were randomized into 3 groups of 8, and a right uncemented total hip replacement was done on each animal. The control group (group 1) received no particulate debris. In groups 2 and 3, a mixture of fabricated ultra-high molecular weight polyethylene, titanium alloy, and cobalt chrome alloy was introduced into the proximal femoral gap. Group 3 also received a once-daily dose of 5 mg of alendronate sodium begun on day 7 and continued until the time of sacrifice.

Radiographically, 1 of 8 control dogs and 6 of 7 dogs from group 2 had periprosthetic radiolucencies with development of endosteal scalloping. In contrast, only 1 of 8 animals from group 3 had periprosthetic radiolucencies. Tissues from both experimental groups had significant macrophage infiltration. Levels of prostaglandin E2 and interleukin-1 were also significantly higher in the experimental groups than in controls. Continuous administration of alendronate effectively inhibited bone lysis for the 24-week duration of the study. Markovich stressed, however, that the clinical usefulness of this treatment is still in question.

Unstable Total Knee Replacement
Instability is the leading cause of failure in TKA.

A patient with preoperative ligament dyslaxity requires prosthetic substitution.

In patients with a primary TKA, a knee that is unbalanced after surgery was not balanced properly during surgery.

Secondary instability after surgery may result from after delayed rupture, wear, or loosening.

Patient history and clinical findings are important in the diagnosis of instability.

Radiographs are not usually helpful. Presentation usually takes the form of dissatisfaction with the knee, multiple falls, instability, pain, and effusion.

Patients are not usually cognizant of instability and usually describe situations in which they descend ramps and their knee tends to give way. Instability must be looked for in flexion, extension, and both positions (global instability).

References
• Borden LS. Diagnosing and treating infection. State of the Art Update in Orthopaedics 2000. Whistler, BC: February 12-16.
• Waldman BJ, Mont MA, Hungerford DS. Total knee arthroplasty infections associated with dental procedures. Clin Orthop. 1997;343:164-72.
• Windsor RE, Bono JV. Infected total knee replacements. J Am Acad Orthop Surg. 1994 Jan;2:44-53.
• Simmons TD, Stern SH. Diagnosis and management of the infected total knee arthroplasty. Am J Knee Surg. 1996;9:99-106.
• Backe HA Jr, Wolff DA, Windsor RE. Total knee replacement infection after 2-stage reimplantation: results of subsequent 2-stage reimplantation. Clin Orthop. 1996; 331:125-31.
• Waldman BJ, Mont MA, Payman KR, et al. Infected total knee arthroplasty treated with arthrodesis using a modular nail. Clin Orthop. 1999;367:230-7.
• D’Antonio J. Looks good, feels bad. State of the Art Update in Orthopaedics 2000. Whistler, BC: February 12-16.
• Markovich GD. Looks bad, feels good. State of the Art Update in Orthopaedics 2000. Whistler, BC: February 12-16.
• Lonner JH, Siliski JM, Scott RD. Prodromes of failure in total knee arthroplasty. J Arthroplasty. 1999;14:488.
• Shanbhag AS, Hasselman CT, Rubash HE. Inhibition of wear debris mediated osteolysis in a canine total hip arthroplasty model. Clin Orthop. 1997;344:33-43.

Basic Techniques in Total Knee Replacement

Templating for Total Knee Replacement

The physical examination should include an analysis of alignment, ligamentous stability, range of motion and muscle strength and function.

These factors, coupled with a radiographic analysis, form the basis for preoperative planning.

Preoperative analysis radiographic analysis: standing anterior-posterior (AP) view, lateral view, and patellar-femoral view.

Survivorship of TKA is directly related to appropriate alignment and balance.

Surgeons should evaluate the biomechanics of knee alignment and determine the proper position of the implant on the mechanical axis. A long-standing radiograph should be obtained.

The process of establishing a femoral cut.

The distal femoral cut is not only important for maintaining varus and valgus positioning but also for maintaining the level of the joint line.

This is particularly challenging for the valgus knee in which the lateral femoral condyle is distally and posteriorly hyperplastic.

Intramedullary and extramedullary alignment guides can be used to accurately bring the distal femoral cut perpendicular to the mechanical axis in the AP plane.

Posterior condyles affect femoral rotation, especially in the valgus knee.

There are advantages of externally rotating the femoral component to approximately the epicondylar axis.

Varus Knee Management Techniques
Because varus deformity is the most common deformity in osteoarthritic knees, familiarity with medial or varus release techniques is a must for orthopedic surgeons performing TKA.

With a standard median patella approach, the first portion of a medial release is performed when the deep portion of the medial collateral ligament is released.

Some surgeons favours a subperiosteal release that does not include the pes anserinus (PES) insertion.

This release is carried posteriorly to include the semimembranous insertion on varus knees but not valgus knees.

The second portion of the release is removal of osteophytes that tent the medial collateral ligament.

With severe deformities, the posterior medial capsule must be released subperiosteally from the tibia to allow correction of the deformity.

The true medial release is performed for further correction, subperiosteally, distal to the PES insertion (but deep to the PES insertion) until the desired correction is obtained.

If medial release for a varus deformity is done in a step-wise and graded fashion, it can titrate the correction needed and allow normal ligamentous balance.

Valgus Knee Management Techniques

The valgus deformity is more complex and difficult than that done in varus knees.

Most surgeons prefer the median parapatellar incision over the median incision because this technique is easy. First, place the alignment jigs for bony cuts. Once the cuts are done, balance the soft tissues. Release the iliotibial band off Gerdy’s tubercle while the lateral capsule is released from the tibia to the posterior lateral corner.

High valgus deformities require a lateral collateral ligament and popliteus, in that order, to be released from the epicondyle on the femur.

More release can be obtained by taking down the intramuscular septum and lateral gastrocnemius.

The posterior cruciate ligament plays a role in maintaining high valgus deformities.

Thus, resection of this ligament is usually required.

A lax medial collateral ligament may also contribute to this type of deformity.

References
1. Morawa MD. Templating for total knee replacement. State of the Art Update in Orthopaedics 2000. Whistler, BC: February 12- 16, 2000.
2. Reilly DT. Varus knee management techniques. State of the Art Update in Orthopaedics 2000. Whistler, BC: February 12-16, 2000.
3. Wright RJ. Valgus knee management techniques. State of the Art Update in Orthopaedics 2000. Whistler, BC: February 12-16, 2000.

Compartment Syndrome

Compartment syndromes develop when the pressure in closed compartment (such as the four compartments of the leg, the anterior or posterior compartment of the thigh, or the three compartments of the forearm) rises to the point that the microvascular circulation of the muscles and nerves in the compartment are compromised.

Pathophysiology

Compartment syndromes develop when the pressure in closed compartment rises to the point that the microvascular circulation of the muscles and nerves in the compartment are compromised.

Normal compartmental pressure is 0 to 10 mmHg. When the tissue pressure rises to between 10 mm Hg and 30 mm Hg of the diastolic pressure, the perfusion of both muscle and nerve is compromised and ischemia occurs.

Important things to remember:

1. With complete ischemia, muscle remains viable for up to 3 to 4 hours without irreversible damage.
1. At 6 to 8 hours of complete ischemia, there is variable recovery.
2. More than 8 hours of complete ischemia causes irreversible muscle injury.
1. Peripheral nerves show conduction changes after 1 hour of total ischemia, the neurons and supporting structures can sustain up to 4 hours of total ischemia with a reversible injury pattern (neuropraxia – conduction defect with Wallerian degeneration).

Presentation

Patients with compartment syndrome present with severe pain that is out of proportion to their injury. The evaluation of patients is difficult and deceiving as the clinical picture can be variable. The amount of pain must be assessed carefully, and assessments should be made at multiple times, ideally by the same individual or with carefully documented progress notes. Pain is often intense, and patients with a fully evolved compartment syndrome have difficulty lying quietly – most resist the clinician palpating the leg.

The key historical finding is extreme pain. Therefore, clinicians must be extremely careful not to over medicate a patient with analgesics because medications mask the compartment syndrome.

Physical Examination

5 steps of examination:

Step 1. Visually inspect the involved limb. Does the limb appear swollen? With marked swelling, the limb will often have a circular appearance and the skin may be taut and shiny without wrinkles.

Step 2. Palpate each compartment. Is there extreme pain with palpation? Is the compartment soft or hard?

Step 3. Test motor function and grade on a scale of one to five. First ask the patient to flex and extend the digits of the involved joint. This test checks if the involved muscles move easily through the compartment. If the patient can easily flex and extend, then swelling in the compartment is probably not severe. Next, test the muscle group and grade the strength.

Step 4. Passively flex and extend the digits or joint, assessing for pain. Extreme pain on passive flexion and extension is a sign of impending compartment syndrome. The tissue pressure in the compartment has risen to the point that there is severe pain with excursion of the muscle and tendons throughout the compartment.

Step 5. Test sensory nerve function by assessing sensibility of the nerves that travel through the compartment. The ability of the patient to feel light touch should be checked first and compared from side to side. If light touch cannot be felt, then one should measure the ability of the patient to detect pin prick. One should also assess for paresthesias and dysesthesias.

Assessment and Decision-Making

After examining the patient, the clinician must decide whether the patient has: 1) no evidence of a compartment syndrome, 2) a possible or probable compartment syndrome, or a 3) definite compartment syndrome.

No evidence of a compartment syndrome
In this scenario, the patient does not have pain out of proportion to injury; the involved compartment is soft, or, if swollen, the amount of swelling is in proportion to the injury; and palpation of the compartment does not produce intense pain. Motor function is normal and any weakness noted should be within the limits one would expect for normal pain and weakness secondary to the injury.

Possible or probable compartment syndrome
In this scenario, the clinician is unsure whether the patient has elevated tissue pressure, which may indicate a compartment syndrome. The patient may have any combination of pain out of proportion to injury, a tense or painful compartment, loss of motor function or sensation, or pain on passive stretch of the muscle of the compartment. To determine whether there are elevated pressures within the compartment, the clinician must measure the pressures within the compartment. Once the compartment pressures have been measured, the clinician then compares the pressures to the diastolic pressure and makes a decision as to whether a compartment syndrome is present.

Definite compartment syndrome

A definite compartment syndrome is present when the patient has severe pain out of proportion to injury, severe pain on passive stretch of the compartment and tenseness.There may be loss of neurologic function (motor or sensory changes).

The patient should be scheduled for immediate fasciotomy of the involved limb. Compartment pressures are measured to confirm the clinician’s diagnosis. The pressure measurements are performed either at the bedside or in the operating room.

Tissue Pressure Measurement

Several instruments are used to measure tissue pressure. One may use a manometer, which is an electronic device such as is available in the intensive care unit, or a custom application such as the Stryker tissue pressure measurement device.

When measuring tissue pressure in a patient with a tibial fracture, the measurement should be done at the level of the fracture.

Indications for fasciotomy

The indications for fasciotomy have varied in the literature. Some authors have recommended an absolute tissue pressure measurement, while others have advocated determining the gradient by comparing the tissue pressure to either the diastolic pressure or the mean arterial pressure. The diastolic pressure is most commonly used because one does not have to do a calculation to determine mean arterial pressure (mean arterial pressure is the diastolic pressure plus one third of the difference between the systolic and diastolic pressures).

An important point to remember is that basic science studies have shown that normal muscle perfusion remains intact with tissue pressures within 10 mm Hg of the diastolic pressure. With injured muscle, the threshold decreases to within 20 mm Hg of the diastolic pressure. With this basic science knowledge, many authors now recommend fasciotomy when the tissue pressure is within 30 mm Hg of the diastolic pressure.

Locking Plate

Locking plates are most often used as a bridging plate in fractures with bone loss and short articular fragments.
The working length of a plate includes the portion of the plate that is unsupported by bone. The longer the segment of unsupported bone, the greater is the risk of failure.

Locking plates have become a popular, effective method of stabilizing metaphyseal/epiphyseal fractures with comminution and short articular fragments.

Important biomechanical features of locking plates include

* Locked screws can function as individual blade plates in the distal fragment.

* Locking plates can effectively serve as bridge plates, providing excellent fixation in short distal articular fragments.

* Compression of the plate against the bone is less than that of conventional plating, resulting in less devascularization of the underlying cortex.

* There is no toggling between the locked screws and the plate.

* The pullout strength of a locked unicortical screw is approximately 60% of a standard bicortical screw.

* Locking plates are similar biomechanically to an external fixator.

* Moment arms are less because the plate is closer to the bone’s neutral axis than the connecting bar of the external fixator.

Cartilage Injuries in the Athlete

Author: Satish Kale

Introduction

With a global increasing in sporting activity there is a corresponding increasing in the incidence of joint trauma and consequently cartilage injuries. As patients get more demanding and want to return as quickly as possible to their pre-injury activity levels, it is imperative that techniques are discovered and developed to treat these injuries in an emergent way.

Much progress has been made but the ultimate dream of cartilage self-induced regeneration has remained largely utopian. Articular or hyaline cartilage is an extremely smooth, hard material, made up of the protein collagen, which lies on a bone’s articulating surfaces. Its function is to allow for the smooth interaction between two bones in a joint and in spite of being only a few millimeters thick has an amazing resilience to compressive forces. Thus, if injured it can lead to impairment in the fluidity of joint movement. In addition articular cartilage is extravascular, meaning that it has no direct blood supply. This means that once injured it is extremely slow to heal.

Histology of Articular Cartilage

The mechanical and structural capacity of the articular cartilage is dependent on the integrity of its extracellular matrix. Chondrocytes sparsely distributed throughout a matrix of structural macromolecules work together with a hydrated extracellular glycosaminoglycans to attract and then sequentially extrude water. Water constitutes between 65-80% of the entire wet weight of articular cartilage and is about 15% more concentrated at the surface than in the deeper zones. Extracellular components of collagen, proteoglycans, non-collagenous proteins and water combine to provide the shear, compressive, and permeability characteristics of cartilage. It is the composition and highly complicated interaction of these components that makes regeneration and replacement techniques challenging.

Functions of the Articular cartilage

The functions of articular cartilage include load transmission and distribution, smooth articulation, and aid in lubrication. Load transmission and distribution is due to the ability of the structural matrix to deform, which leads to increased joint contact areas and distributed mechanical stresses. It also has the ability to respond to applied loads through fluid exudation and redistribution within the interstitial tissue. Some texts also mention about a proprioceptive function, which aids in recognizing and limiting joint-deforming forces and induce protection.

What is the Cartilage Crisis?

Most of the joints in the body are synovial joints, that is movable, lubricated joints which are able to provide normal pain-free movement because of the unique properties of the articular cartilage. The articular cartilage covers and protects the ends of the bones in joints. The knee is the largest synovial joint. At the top of the knee are the massive quadriceps muscles, which cause the knee to extend. The hamstring muscles are at the back of the knee and cause it to flex. The knee joint has a synovial membrane, which is tissue that lines the noncontact surfaces within the joint capsule. The ends of the tibia, femur, and the patella are covered by articular cartilage. This is the structure that described to be in crisis.

Causes of Cartilage Damage

The common causes of cartilage damage are:

1. Trauma and fractures

2. Surgery

3. Degenerative

4. Disease and Obesity

5. Regenerative

Diagnosis and Investigations Arthroscopy

The articular cartilages are divided into 5 compartments including lateral and medial tibial, lateral and medial femoral and patellar compartments.

The articular cartilages are graded using a modified Outerbridge classification.

Grade 0 indicated intact cartilage,

grade 1 chondral softening with normal contour,

grade 2 superficial fraying,

grade 3 surface irregularity and thinning

grade 4 full thickness cartilage loss.

The grades of articular cartilage were compared with cartilage volume measurements.

MRI

MRI, by virtue of its superior soft-tissue contrast, lack of ionizing radiation and multiplanar capabilities, is superior to more conventional techniques for the evaluation of articular cartilage unlike radiography, MRI provides:

A. Provide direct visualization of the hyaline cartilage (as well as the meniscus and bone)

B. Accurate quantification with sensitivity to change

C. MRI is also less subject to positional change, which is a particular problem in the interpretation of small changes in radiological measures in longitudinal studies

Articular cartilage lesions may be categorized as degenerative or traumatic in cause. Early degenerative disease may be seen on MRI as fibrillation or surface irregularity, cartilage thinning or thickening or intrachondral alterations in signal intensity.

Advanced degenerative chondral lesions manifest on MRI as multiple areas of cartilage thinning of varying depth and size, usually seen on opposing surfaces of an articulation. Other associated MRI findings of degenerative cartilage disease include central and marginal articular osteophytes, joint effusion, and synovitis.

In contrast, traumatic chondral lesions generally manifest on routine clinical MRI as solitary focal cartilage defects with acutely angled margins.

Traumatic chondral injuries are typically the result of shearing, rotational, or tangential impaction forces and often result in high-grade partial- or full-thickness cartilage tears or in osteochondral injuries of cartilage and the underlying subchondral bone.

As a rule, recognition of a traumatic chondral defect should prompt careful inspection of the joint for a displaced intraarticular chondral body.

Cartilage Mapping

Using specialized image processing algorithms, individual structures, such as the articular cartilage, can be isolated from a MR image and quantified in a variety of ways, including total volume measurement and thickness mapping.

The precision error for measuring cartilage volume is approximately 2 %, while that for cartilage thickness mapping is 0.3 mm. Pressure Point Maps Newer MRI machines and specialized sequences allow application of stress to the knee while the patient is in an MRI scanner. It has the ability to simulate squatting and stresses with the patient lying down.

Scoring Cartilage Injuries

At the Symposium of the International Cartilage Repair Society (ICRS) in 1997, a working group presented The Cartilage Standard Evaluation Form, adapted from the International Knee Documentation Committee system. Patient data such as cause of injury, age at the occurrence of injury, onset of symptoms, sporting activities, knee pain, subjective knee function (percentage of function compared to the normal knee), previous surgery, and activity level were included.

According to this system, the depth of cartilage defects is ranked on a 4-grade scale.

The size and the anatomical localization further describe the defects.

The defects are also outlined by the surgeon on standard grid maps including frontal and lateral views of the articular surfaces of the knee.

ICRS Grading

Grade I is superficial fissuring of the articular cartilage.

Grade II is fissuring extending to less then half the normal cartilage depth.

Grade III is fibrillations in the articular cartilage greater than half the normal cartilage depth and up to but not through the subchondral plate.

Grade IV is significant lesions penetrating the subchondral bone.

Treatment

Treatment of articular cartilage defects in the knee has been attempted in numerous studies and all with varying levels of success.

Treatment can be directed at either treating the symptoms or trying to affect articular repair or regeneration

Repair refers to the restoration of a damaged chondral surface with new tissue that resembles but does not duplicate the structure, biochemical makeup, function and durability of articular cartilage.

Regeneration denotes the formation of new tissue indistinguishable from normal articular cartilage.

There is also the component of other associated pathology in conjunction with focal articular cartilage damage.

A few of the more common treatment methods are noted below.

Lavage:

Lavage rids the knee of loose articular debris and inflammatory mediators that are known to be formed by damaged synovial joints. When arthroscopic lavage was performed in conjunction with mechanical debridement, there were improved results with about 88% short-term improvement. The results vary widely.

Bone marrow stimulation techniques:

These procedures are theorized to stimulate and mobilize the mesenchymal stem cells to differentiate into cartilaginous repair tissue. Once disruption of the vascularized cancellous bone has occurred, a fibrin clot is formed and pluripotent cells are introduced into the area.

These cells eventually differentiate into chondrocyte-like cells that secrete type I, II and other collagen types as well as cartilage specific proteoglycans after receiving mechanical and biological cues. The cells produce a fibroblastic repair tissue that on appearance and initial biopsy can have a hyaline-like quality.

Unfortunately, over time the histological characteristics change into more predominantly fibrocartilaginous tissue.

Abrasion arthroplasty consists of debriding the articular defect to a normal tissue edge so that fresh collagen can be produced in the fibrin clot.

The surface of the subchondral bone is exposed and penetrated to a depth of about 1 mm.

Various reports show 12-53% reduced pain post-operatively.

One of the potential problems with abrasion arthroplasty is the cell death produced by the heat of the abrasion burr and thus the destruction of the normal subchondral anatomy may impede any future repair or regeneration efforts.

Subchondral drilling consists of drilling through the defect to penetrate the subchondral bone.

The technique was first popularized in the late 1950’s by Pridie and subsequent findings suggest the repair tissue introduced into the area can look like grossly like hyaline cartilage but histologically resembles fibrocartilage. Drilling also increases the possibility of cell death through heat necrosis.

Microfracture is another such technique in which the lesion is exposed, debrided, and a series of small fractures about 3 to 4 mm in depth are produced with a sharp instrument. Adjacent cartilage is debrided to a stable cartilaginous rim, and any loose fragments and fibrous tissue are removed.

In microfracturing, there is no heat necrosis and the structural integrity of the subchondral bone is maintained. Fibrocartilage is produced and the clinical results remain mixed. Soft tissue and osteochondral grafts: Utilizing either autologous tissue or allografts, these procedures are designed to provide a suitable environment for stimulation of the mesenchymal cells to produce type II collagen fibers.

The success of such approaches is at least in part related to the severity of the abnormalities, the graft quality and technique utilized, age of the patient and correction of associated pathology. Attempts to provide the damaged articular cartilage with a viable durable surface has led to the introduction of soft-tissue grafts consisting of periosteum, perichondrium, fascia, joint capsule and tendinous structures into the defect. A critical component for success with these techniques is that the cambium layer must be placed facing into the joint and the surface must be secured adequately to avoid being knocked loose with joint motion.

The potential benefits include the introduction of a new cell population along with an organic matrix, a decrease in the possibility of degeneration of the tissue before a new articular surface can be produced, and an increased protection of the graft from damage due to excessive loading.

Mosaicplasty:

This technique consists of harvesting a bone-cartilage graft harvested from the posterior aspect of the femoral condyle and transplanted into the defect. The technique is also referred to as “mosaic-plasty” because of the mosaic fashion in which the grafts are implanted into the defect.

Several authors have reported good to excellent results with 70-92% reduction of symptoms and improvement of function in short term observations. This technique has also been shown to restore subchondral bone, improve joint incongruity and actually restore an articular surface.

Osteochondral allograft:

The small number of available graft sites and donor site morbidity could be avoided by the use of fresh or cryopreserved allografts.

However, there are additional problems of allograft rejection, disease transmission, mismatch in sizes and congruity, and sparse supply. Those suffering from primary degenerative arthrosis or those with patella defects do not seem to benefit. Some investigators have found a 63-77% good result from 2-10 years.

Autologous chondrocyte cell transplantation (Auologous Cartilage Implantation ) or ACI:

The limited ability of chondrocyte cells to effectively differentiate, proliferate, and regenerate hyaline cartilage has increased the interest in of transplanting live cells into chondral defects. This technique requires that no penetration of the subchondral bone occur in order to prevent the introduction of blood and the circulating fibrocytes. Short term follow-up reveals newly formed cartilage-like tissue covering about 70% of the transplanted area in animals.

However, the results deteriorate significantly by one year. Two years after transplantation, about 66 % have good to excellent results with histological examination showing appearance of hyaline-like cartilage.

Subsequent research has shown encouraging results regarding the use and efficacy of this technique for focal chondral defects but not for osteoarthritic joints. It is thought that the degradative enzymatic synovial fluid of the arthritic knee is not conducive to cell transfer by this technique.

Steps in ACI

1. Harvesting normal articular cartilage from non- weightbearing sites of the knee by arthroscopy (Diagram A)

2. Extraction of chondrocytes in the laboratory and in-vitro cultivation for 2-6 weeks.

3. Debridement of the articular cartilage defect and harvesting of the periosteum from the tibia. (Diagram B)

4. Suturing of the periosteum over the defect or sealing it using fibrin glue. (Diagram B)

5. Injection of 1 x 106 cultivated dedifferentiated chondrocytes per cubic centimeter under the perisoteum (Diagram B)

Diagram A

Diagram B

Meniscus implantation/replacement:

Due to the complexity of the the tissue, meniscus shape and function has never been able to be modeled or reproduced effectively. It is this inherent intricacy that has eluded practitioners’ ability to provide effective treatment for this condition.

The most common and relatively successful technique to date is the use of allograft meniscal transplantation surgery using a frozen meniscus. Over 1600 such implants have been performed nationwide with only fair follow-up studies conducted on their use and efficacy.

The most common problem post-implantation is shrinkage of the meniscal tissue, yet the results are currently moderately encouraging. Research has shown no reported benefit to using cryopreserved meniscal cartilages. Fresh frozen menisci is currently used. The use of a continuous passive motion machine and a good strengthening program are also critical for success following this procedure.

Carbon Fiber Matrix Implant

Dr. G. Bentley reported 8 year follow-up of carbon fiber matrix implants, noting satisfactory results in 77% of patients overall, with 93% satisfactory results in the treatment of medial femoral condyle lesions.

Rehabilitation after surgery:

The objectives of rehabilitation are:

1. Protecting the joint in the early stages from further mechanical injury via the appropriate use of braces, crutches or sticks.

2. Reducing swelling and inflammation as soon as possible to allow full mobilisation

3. Identifying infection early before it has a chance to spread

4. Restoring range of motion (ROM) to prevent later permanent limitation of flexion or extension. This also rebuilds muscle strength and prevents adhesions.

5. Restoring priprioception and restoring normal gait patterns.

Conclusions

Cartilage repair techniques have now evolved to make cartilage autotransplant and chondrocyte culture a viable and option for cartilage defects in the athlete. Obviously, patient selection remains the single most important factor for the results in cartilage repair studies. As seen in various trials and studies, patients with cartilage defects are not a uniform group, and this should be taken into consideration. Cartilage injuries in the athlete are commonly associated with other pathological conditions of the joint such as ACL ruptures and meniscal injuries and they need to be addressed primarily for improving outcomes.

Recommended Reading

1. Recht MP, Resnick D. MR imaging of articular cartilage: current status and future directions. AJR 1994;163 : 283-290

2. Xia Y, Farquhar T, Burton-Wurster N, Lust G. Origin of cartilage laminae in MRI. J Magn Reson Imaging1997; 7:887 -894

3. Lehner KB, Rechl HP, Gmeinwieser JK, Heuck AF, Lukas HP, Kohl HP. Structure, function, and degeneration of bovine hyaline cartilage: assessment with MR imaging in vitro. Radiology 1989;170 : 495-499 International Cartilage Repair Society. http://www.cartilage.org

4. Rehabilitation following microfracture/ abrasive chondroplasty or mosaicplasty to femoral condyle, 2003 RJ&AH Orthop & District NHS Trust Oswestry.

5. New techniques for cartilage repair and replacement , Kevin R. Stone, M.D. , Michael J. Mullin, ATC, PTA , The Stone Clinic, 3727 Buchanan Street • San Francisco CA 94123

6. K. A. Turman and M. D. Miller, What’s New in Sports Medicine, J. Bone Joint Surg. Am., January 1, 2008; 90(1): 211 – 222

7. Brittberg M, Lindahl A, Nilsson A, et al. ‘Treatment of deep cartilage defects in the knee with autologous chondrocyte transplantation.’ N Engl J Med 1994; 331:889-895.

8. Gillogly S, Voight M, Blackburn T. ‘Treatment of articular cartilage defects of the knee with autologous chondrocyte implantation.’ Jour of Orthop and Sports Physical Ther 1998; 28:241-251

9. Minas T. ‘Chondrocyte implantation in the repair of chondral lesions of the knee: economics and quality of life.’ Am J Orthop. 1998 Nov;27(11):739-44

10. Bentley G, Minas T. ‘Treating joint damage in young people.’ BMJ. 2000 Jun 10;320(7249):1585-8.

11. Ho SS, Luo J, Haydon R, et al. Characterization of chondrocyte scaffold carriers for cell-based gene therapy in articular cartilage repair. Program and abstracts of the American Orthopaedic Society of Sports Medicine Annual Meeting; July 14-17, 2005; Keystone, Colorado.

12. Potter HG. Symposium: MRI-T2 mapping [of articular cartilage]. Program and abstracts of the American Orthopaedic Society of Sports Medicine Annual Meeting; July 14-17, 2005; Keystone, Colorado.

Knee Arthroscopy

Nowadays knee arthroscopy as a diagnostic procedure has evolved from an inpatient procedure to one performed as a day-care procedure under regional or even local anaesthesia.

Meniscal repair

Since the meniscus is paramount to effective shock-absorbing function of the knee joint, it is always recommended to preserve the meniscus rather than debride it. Various techniques are now available for arthroscopic meniscal repair. The Bio-absorbable Meniscal Arrows are made up of copolymers ( 96% poly-L, 4 %Poly–D Lactic acid) which provides high strength microstructure. After the tear is reduced into position with the help of a probe ,the arrow is introduced through the cannula to fix the tear.

Arthroscopic Meniscal Transplantation

The indication for this procedure is a patient with meniscectomy or a severely injured meniscus, skeletally mature with stable ligaments and a normal femorotibial alignment. This technique involves use of deep frozen cadaver allograft tissue thoroughly thawed to eliminate crystalline water content. The original meniscal remnants are debrided except for the peripheral border. With a hand gouge and burr a trough is prepared to receive the allograft bone. The allograft bone is fixed to the tibial bone trough by means of pull out sutures.

Chondral injuries

According to recent research, up to 10 to 12% of individuals present with chondral injuries. Those which are symptomatic or in the weight-bearing zone manifest as swelling and knee pain. The natural history of untreated lesions is progression and increasing disability. These are classified by the modified Outerbridge classification into grades 1 to 4 depending on the severity. In Outerbridge grades 2 and 3 lesions, with a properly tracking patella, debridement removes fibrillation and provides a stable rim of chondral tissue.

Recent studies suggest that bipolar radiofrequency probes are superior to mechanical shavers for articular cartilage debridement. This procedure is a valuable technique particularly in adolescents and young adults  Autologous chondrocyte implantation (ACI) beneath a periosteal patch covering the lesion is increasing being used across dedicated centres across the globe.

The choice of procedure depends on the characteristics of the lesion, patient’s symptoms, age and activity level.

Though Autologous chondrocyte transplantation is presently claimed to have a durable outcome, long term results are not yet clear. With bony defects co-existing with chondral injuries, osteochondral autograft transplant is used in which a bone cone graft capped with healthy hyaline cartilage is harvested from the non weight bearing region of the intercondylar notch and transplanted into the defect. This can effectively delay total knee replacement in the relatively young patient.

For larger defects the technique of “mosaicplasty” is used involving insertion of multiple plugs of osteochondral grafts into the defect.

PCL Reconstructions

Though anterior cruciate ligament reconstruction has been widely practiced using the arthroscope. Increasingly posterior cruciate reconstruction is being attempted rather successfully by the new genre of knee surgeons and arthroscopic reduction and retrograde fixation is being done for large fractured bony fragments which get avulsed with the posterior cruciate ligament.

Intra-articular Fractures

Tibial plateau fractures needing condylar elevation techniques to reconstruct the joint congruity and patellar fractures without major separation and comminution can be reduced under arthroscopic guidance and fixed percutaneously with cannulated screw. It allows clear visualization of the reduction and facilitates early mobilization of the knee.