Knee Arthrofibrosis

The term Knee arthrofibrosis has been used to describe a spectrum of knee conditions in which loss of motion is the major finding. It is perhaps best defined as a condition of restricted knee motion characterized by dense proliferative scar formation, in which intra-articular and extra-articular adhesions can progressively spread to limit joint motion. This dense scar tissue can obliterate the parapatellar recesses, suprapatellar pouch, intercondylar notch, and eventually the articular surfaces. Patella infera and chronic patellar entrapment also may develop as a consequence of this process.

Knee Arthrofibrosis was described as the fibroplastic response of the joint to trauma in 1951.

Knee Arthrofibrosis Causes

Knee Arthrofibrosis may occur as the result of the inflammatory cascade after injury or operative treatment. Although inflammation is undoubtedly present in a large number of individuals, it is not clear why an aggressive form of this condition may develop in some patients.

To diagnose Knee arthrofibrosis accurately, other causes of restricted active and passive motion of the knee must first be eliminated. Mechanical causes include loss of articular congruency (e.g., as a result of fracture, meniscal tear, or loose body), interruption of the extensor or flexor mechanism, substantial effusion, or nonisometric placement of a graft during reconstruction of the ACL.

Some investigators believe that an ACL reconstruction performed within 3 weeks after an injury may increase the likelihood of Knee arthrofibrosis although others disagree. Poor or unsupervised rehabilitation preoperatively or postoperatively, with delayed motion protocols, may further increase the risk.

Clinical Evaluation

Symptoms vary and often do not correlate with the severity of the condition. Since knee arthrofibrosis usually occurs after trauma or an operative procedure, pain and stiffness may be the initial symptoms:

1. The presence of pain may complicate preexisting knee stiffness. Although pain can be present early, it often becomes more prominent when joint degeneration and arthritis occur because of long-standing Knee arthrofibrosis. Pain may also be constant, especially when it is associated with complex regional pain syndrome (CRPS).
2. Decreased ROM
3. Decreased patellar glide from cranially to caudally (best test)
4. Decreased patellar tilt
5. Warmth and swelling with surrounding atrophy
6. Flexed-knee gait
7. Shelf sign (late finding).

See Also: Complex Regional Pain Syndrome (CRPS)

Patients with Knee arthrofibrosis present with persistent stiffness, pain, and typically a painful flexed-knee gait. Warmth and swelling will be present in the active phase, and there will commonly be surrounding atrophy. Notable physical findings include decreased ROM and decreased patellar glide. However, one must be aware that during the normal healing response, the patella will exhibit decreased mobility between weeks 4 and 12, with a gradual return of mobility as week 16 approaches.

Quadriceps function can be decreased or absent because of pain. As function of the quadriceps muscle decreases, the ability of the muscle to act as a shock absorber is lessened, which may lead to additional articular degeneration. Often, the knee is held in a flexed position, which encourages tightening of the posterior part of the capsule and the hamstrings.

Crepitus and weakness are frequently present with swelling following prolonged standing or walking. Even when the patient does not have pain, loss of motion and quadriceps weakness can be substantial impediments to the performance of activities of daily living. An antalgic, flexed-knee gait is often seen. Although effusion may be present, swelling is more often a result of inflamed, thickened capsular and pericapsular tissues.

Active and passive knee flexion and extension often are restricted in a capsular pattern, and the mediolateral and superoinferior patellar glides are reduced. This restriction of passive motion often has a spring-like end-feel, reflecting the density and stiffness of the thickened, inflamed, or scarred peripatellar tissue.

Imaging

Standard x-rays: Anteroposterior, bent knee posteroanterior, and Merchant view x-rays should be obtained, in addition to an excellent lateral image of the knee in 30 degrees of flexion. The lateral image is crucial to evaluate for patella infera, which can be measured using the modified Insall-Salvati method.

The length of the patella tendon is measured from its origin from the inferior pole of the patella to its insertion at the proximal pole of the tibial tubercle. The length of the patella is then measured at its greatest diagonal length from its superior to inferior pole. The normal ratio of length of the patellar tendon:length of the patella should be approximately 1:1, with some minor gender variation. A ratio of less than 0.8 indicates patella infera.

Magnetic resonance imaging (MRI): MRI can be helpful to evaluate for causes of anterior impingement, including improper graft placement and exuberant scar formation anteriorly as well as the presence of a “pseudopatella tendon”.