Lateral Patellar Compression Syndrome

                                  Dr. KS Dhillon

Among young and active individuals anterior knee pain is one of the most common musculoskeletal complaints (1-3). The constant anterior knee pain can be disabling and it can limit daily functional activities. The pathogenesis of anterior knee pain is multifactorial. Primary contributors to this pain include patella instability and overload of the subchondral bone (4). In some patients with anterior knee pain, no predisposing subluxation can be found (5,6). Patellar compression syndrome also previously known as excessive lateral pressure syndrome is a disorder that is associated with overload and increased pressure on the lateral facet due to pathologic lateral soft-tissue restraints (5,7,8). Patellofemoral malalignment causes an increase in Q angle which results in greater surface contact between the lateral aspect of the patella and the lateral condyle of the femur during weight-bearing activities (9).

When the knee is flexed there is an increase in posterolateral compressive forces on the lateral aspect of the patella. This is consistent with the clinical observation that most patients with anterior knee pain tolerate prolonged knee flexion poorly (5,7,10).  Since the contact pressure over the lateral patellar facet increases as knee flexion progresses, a more specific term to identify the pathologic process would be lateral patellar pressure in flexion or lateral pressure in flexion (LPIF).

Arthroscopic lateral retinacular release is a common procedure that is used to alleviate the pathologic forces on the patella in LPIF. This procedure can however be associated with a serious complication i.e. iatrogenic medial patellar subluxation. Medial patella subluxation can worsen the patient’s knee pain and it will require further stabilization procedures (11-13). The arthroscopic release that is often done usually does not extend distal enough to relieve the pressure in flexion (14). The length of the release, especially in the distal direction determines the biomechanical effects of lateral release. Most lateral releases are performed with the knee in extension and not in flexion which is the position of maximum contact pressure. The release extends inferiorly only as far as the joint line or anterolateral inferior arthroscopic portal. The clinically necessary

amount of release is not known with certainty. Extending the release distally to the level of the tibiofemoral joint line does result in measurable increase in patellar mobility.

To overcome the shortcomings of the traditional arthroscopic lateral release procedures a new technique was developed to perform a lateral release. The release is performed open with the knee in flexion. The lateral release is then repaired with a rotation flap of the iliotibial band to close the defect and prevent patellar subluxation. This technique decreases lateral patellar pressure and centers the patella in the trochlear groove thereby reducing the risk of iatrogenic patellar instability. 

Diagnosis

Patients with LPIF complain of constant anterior knee pain. The pain is localized at the inferomedial aspect of the patella and the anteromedial joint line, in the course of the medial patellotibial ligament. The patients have pain with prolonged knee flexion or when they climb or descend stairs. Knee extension is limited and painful. The pain is not relieved by bracing, medications, or physical therapy. Lateral patellar compression in flexion can be confirmed by clinical examination. There is focal tenderness at the inferomedial aspect of the patella and/or the anteromedial joint line. There is no joint effusion or crepitus. The patella is stable in both flexion and extension. LPIF can be tested by manually centering the patella in the trochlea at 45 degrees of knee flexion and during active knee extension and flexion. 

The knee is examined with the patient in a seated position. The patient will have pain at rest. The pain can be reproduced with knee motion. The pain will limit extension and it will increase as the knee approaches 90 of flexion. Attempts to center the patella in the trochlea by pushing the patella medially will usually provide immediate relief of the pain by reducing tension on the medial patellotibial ligament. Full knee extension is possible.

When centering the patella decreases the patient’s pain and allows a

greater pain-free range of motion, particularly in extension, LPIF is likely.

To verify the diagnosis of lateral patellar pressure in flexion the patient is examined under anesthesia. Metcalf (15) and other authors (16) described the lateral overhang sign seen during diagnostic arthroscopy. Mild overhang is present in most normal knees in full extension. Patella overhang that includes the complete lateral facet or 50% of the surface of the patella is considered abnormal. Lateral-sided tightness can be seen when the patellofemoral articulation is viewed from the anteromedial arthroscopic portal. In knee extension, the lateral retinaculum may or may not be tight. With flexion of the knee, the inferolateral corner of the patella begins to tighten. When flexion of the knee increases, the lateral facet of the patella becomes compressed over the lateral femoral condyle. At 90 degrees of knee flexion, the patella is tight over the lateral femur and it is not congruent with the trochlea. Pressure leads to a concave shape of the lateral facet. 

Surgical Technique

With the patient in a supine position, a tourniquet is applied on the thigh. Arthroscopy is performed and the intra-articular findings are noted.

Evaluation of patellar alignment and position, the shape of the patella and the femoral trochlea, laxity on both the lateral and medial sides, and the degree of lateral-side tightness is carried out. Assessment of patellar stability is also carried out. The patellofemoral, lateral, and medial compartments are examined for the presence of chondral injuries.

Loose bodies are removed and chondroplasty is performed if necessary. Meniscal pathology is treated if necessary. A midline skin incision is made. The patella and patellar mechanism from the patella to the tibial tubercle is exposed. The lateral side of the patellar tendon is freed. The lateral retinaculum is opened at the inferolateral tip of the patella. The release is carried far enough proximally to allow the patella to center in the trochlear groove. There is no need for

the release to extend past the superior pole of the patella. A tibial osteotomy may be necessary if there is excessive lateralization of the tibial tubercle. The tibial tubercle osteotomy allows the tubercle to be placed anteriorly and medially. If there is patella baja, the tubercle is recessed more proximally. The patellar tendon is then freed on the medial side. The tibial tubercle is cut with a saw and rotated medially and anteriorly. It may be moved upward or downward. The alignment and pressure on the patellar tendon can be corrected by fixing the tubercle in the desired position. The tubercle is fixed to the tibia with 2 screws. The bony defect created on the lateral side can be filled with synthetic bone graft. After the tibial tubercle is fixed, the lateral release is repaired by rotating a flap of adjacent iliotibial band to fill the defect. This prevents lateral side laxity and medial subluxation of the patella. 

If the lateral side is very lax, the lateral release is extended into the vastus lateralis tendon. The tendon can be overlapped. This will tighten the lateral structures above the patella. The lower part of the lateral release is repaired. 

Repeat arthroscopy is performed to see resolution of the LPIF and to see if the patella is centered within the femoral trochlea. The patella is examined for stability. Lateral and medial forces are applied to the patella in full extension and 30 degrees of flexion to assess for medial and lateral patellar stability. If necessary, soft-tissue reconstructions are performed.

Postoperatively a knee brace is applied and the patient is taught active range-of-motion and quadriceps-strengthening exercises. The patient is allowed to weight bear as tolerated with crutches for 2 to 4 weeks. The knee brace is removed when the patient has gained good quadriceps control.

Discussion

There is a need to know the normal anatomy and kinematics of the patellofemoral joint to understand the pathologic process of LPIF. The lateral retinaculum is a richly innervated connective tissue structure. It is located on the lateral aspect of the knee (4). The lateral retinaculum is composed of 2 layers (17,18). The superficial layer is composed of oblique fibers of the lateral retinaculum originating from the vastus lateralis fascia and iliotibial band and inserting into the patella tendon and the lateral margin of the patella. The deep layer of the retinaculum consists of several structures. These include the transverse and lateral patellofemoral ligaments and the patellotibial band. The deep layer is oriented longitudinally with the knee extended but exerts a posterolateral force on the lateral aspect of the patella as the knee goes into flexion (10).

The lateral and medial forces are balanced in a normal knee. The patella glides smoothly in the femoral trochlea. Any change in this mediolateral equilibrium can lead to instability and pain (14). When the knee is extended the patella lies laterally, but as the knee is flexed, the patella moves medially and it engages in the trochlea. With further knee flexion the patella flexes and translates distally (19). With the knee in 45° flexion, the patella is fully engaged in the trochlear groove. 

As the knee flexes more the patella moves laterally. There is a progressive increase in patellofemoral joint contact area from 0° to 60° of knee flexion. There is greater lateral facet contact area compared with the medial facet contact area as the knee flexes more.

Lateral retinacular release is carried out to relieve peripatellar pain and to reduce the pathologic lateral forces contributing to abnormal lateral pressure. Biomechanical effects of the lateral release are related to the length of the release, especially in the distal direction. The arthroscopic lateral release is performed with the knee in extension and not in flexion. The release extends inferiorly as far as the joint line or anterolateral inferior arthroscopic portal (14).

Marumoto et al (14) carried out a biomechanical comparison of lateral releases. They found that release of the patellar lateral restraints, when extended down to the tibial tubercle, was significantly increased compared with a release that extends only to the level of the anterolateral inferior arthroscopic portal. 

Ostermeier et al (7) investigated the influence of lateral retinacular release and lateral and medial retinacular deficiency on patellofemoral position and retropatellar contact pressure. Their lateral release extended from 20 mm proximal to the proximal aspect of the patella to the Gerdy tubercle. They found that lateral retinacular release could decrease pressure on the lateral patellar facet in knee flexion in patients with anterior knee pain without instability but with overload of the lateral facet of the patella. When lateral release in flexion is done, the posteriorly directed force of the lateral retinaculum and iliotibial band is removed. The patella then moves in an anterior direction, alleviating the pressure on the lateral facet.

Powers et al (18) found an increase in patellar tendon tension after the removal of the peripatellar retinaculum. This indicates that the lateral retinaculum acts as a load-transmitting structure within the extensor mechanism. They found that at 60° of knee flexion, there was a 9.6% increase in patellar tendon tension when the retinaculum was removed. They were of the opinion that with increasing knee flexion angles, there would be increased load sharing of the retinaculum. Releasing the lateral retinaculum in patients with anterior knee pain may impair its load-sharing capability and increase the forces on the patellar tendon. This increase in patellar tendon tension would lead to greater joint compression. If the lateral release is repaired with an iliotibial band rotation flap, the load-sharing function of the lateral retinaculum can be restored and patellofemoral contact pressures normalized.

The position of the tibial tubercle can contribute to overloading the cartilage on the lateral facet of the patella and cause pain (20,21). Anteromedialization of the tibial tubercle can be done to improve patellofemoral alignment (22). In patients with excessive lateralization of the tibial tubercle, lateral retinacular release alone is not sufficient to adequately reduce pressure on the lateral facet of the patella. In such patients, a tibial tubercle osteotomy is needed. Medializing the tibial tubercle by 1 cm significantly reduces the maximum lateral pressure by 15% to 20% for intact cartilage without overloading the medial cartilage (23). The degree of anteromedialization will depend on the amount of correction needed. Some of the patients have excessive lateralization and require significant correction. Others require a more modest correction. The Q angle is reduced to 0 degrees by correctly aligning the bony tubercle and the patellar tendon. Both under-correction and over-correction are undesirable for improving patellofemoral alignment and normalizing contact pressures.

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