Lateral retinaculum contributes not only to medial restraint of the patella but also to lateral restraint. Selective cutting studies in cadavers have shown that lateral retinaculum release (LRR) at mid-patellar level caused significant reduction of lateral stability between 30° and 90° of knee flexion.¹ Thus, the patella with its medial and lateral restraints should be looked upon as a canopy tent on straight poles. Severing one side of the poles could make the tent unstable in either or both directions (Figure 11.1).

Medial patellar subluxation (MPS) is a disabling condition that is usually iatrogenic in its nature, following a wide LRR.²

The first case of traumatic MPS (without lateral release) was reported in 1869.³

LRR was first described by Pollard in 1891 and popularized by Merchant and Mercer in 1974. The first case of MPS following lateral release was reported by Betz et al in 1987, following which a large series of 30 knees with MPS was reported by Hughston and Deese in 1988.²,⁴,⁵

The casual approach toward LRR as a minor procedure or procedure to address anterior knee pain or instability owing to varied (and sometimes unknown) etiology led to the creation and recognition of MPS entity. On a technical note, extended LRR, including release of vastus lateralis tendon from the superolateral aspect of the patella, would lead to a loss of dynamic control of patellar stability, resulting in MPS. Thus, both inappropriate indications and/or technique of lateral release could potentially lead to MPS.²,⁶

The recommended technique of extending the release in a stepwise manner until “turn-up” sign of 90° patellar rotation to ensure decompression led to lateral over-release and resultant MPS, quadriceps atrophy, and worse clinical outcomes. It should be avoided. Instead, a limited lateral release without cutting into the tendon of vastus lateralis, to achieve one to two quadrants of medial patellar glide or “turn-up” sign of 45°, would avoid complications. An even better option would be lateral retinacular lengthening, instead of LRR⁷ (see Chapter 12).

MPS is usually characterized by disabling knee pain, severe dysfunction, and/or psychological effects that are out of proportion and worse compared to preoperative symptoms. When compared to typical anterior knee pain, patients with MPS had higher rates of kinesiophobia (100% vs 80%), catastrophizing pain (41% vs 37%), anxiety (59% vs 37%), and depression (24% vs 11%).⁸

MPS could be missed if the physician is not aware of its existence because the symptoms may be vague and nonspecific. It could also be overlooked because the patient may complain of patella moving laterally with early knee flexion. Strong suspicion is necessary on the part of the physician when prior lateral release has been performed. It is not uncommon for the patient to visit multiple physicians till an appropriate diagnosis is established.

Other iatrogenic causes of MPS include overmedialization of tibial tubercle transfer or overtensioning and/or nonisometric femoral fixation during medial patellofemoral ligament (MPFL) reconstruction.

Few cases of spontaneous or traumatic medial subluxation (without prior lateral release) and congenital medial patellar dislocation have been reported.

Of 168 cases of MPS reported in literature (till 2015), 153 (91%) were after lateral release. The lateral release was either isolated or associated with other realignment surgery. Eight cases were post-traumatic, and seven cases occurred spontaneously.⁸

The lateral retinaculum consists of two layers with separate distinct anatomic structures⁹ (Figure 11.2):

The deep transverse retinacular fibers are dense and thick. They are most important in providing resistance to medial patellar translation because they anchor the lateral patella and vastus lateralis tendon.

Staged LRR, especially in its midsection which included transverse fibers, reduced the medial stability of the patella by 7% at 20°, 30°, and 90° of knee flexion, making it easier to sublux the patella medially. An added capsular release reduced the medial stability of the patella at 0° and 20° flexion by 16% compared to intact knee.¹

The term lateral patellofemoral ligament (LPFL) was first used by Reider et al in 1981.¹⁰

There is controversy as to the location and dimensions of LPFL. According to cadaveric study by Merican and Amis, the LPFL is a thickening of the joint capsule, variable in its size and margins.¹¹ It attached to the patella at its widest part. The femoral insertion is at the lateral femoral epicondyle (Figure 11.3).

Cadaveric study by Navarro et al reported LPFL as visible and palpable thickening of the transverse retinacular layer.¹² The mean length of the LPFL was 42.1 mm (from 31 to 53 mm), and the mean width was 16 mm (from 13 to 20 mm). It attached to the patella at its superolateral aspect and inserted into the lateral epicondyle, with a triangular expansion of its fibers that extended posterior and proximal to the epicondyle.

Isometric assessment of LPFL showed that the origin of the ligament is at the lateral epicondyle and its insertion on the patella is at about mid one-third of patellar height.¹³

Recent anatomic study highlighted the variability of attachment of LPFL on lateral epicondyle. The attachment point ranged from 13.1 mm proximal to 11.4 mm distal to the lateral epicondyle and 14.9 mm anterior to 7.3 mm posterior to the lateral epicondyle. In contrast, the insertion onto the patella was more reliable in its middle third.¹⁴

Table 11.1 lists indications and contraindications for LPFL reconstruction.

Patients usually complain of chronic, vague, peripatellar pain, and intermittent swelling.

Other symptoms may include pain with knee flexion activities and difficulty climbing or descending stairs. Symptoms may appear even when walking on flat surfaces.

Patients may describe episodes of giving way and feelings of instability. The patient may be aware of the medial direction of instability, but most often they are not.

The pain is not relieved by medication or physical therapy.

Patients with MPS may exhibit anxiety, depression, or other psychological problems.

Peripatellar tenderness, minimal effusion, or occasional patellofemoral crepitus

Marked atrophy and retraction of vastus lateralis tendon, resulting in palpable and visible void at its insertion onto the patella, in patients with prior LRR

Tenderness at the site of lateral release.

Active and passive range of motion may be painful during the first 30° of knee flexion. Patient may complain of feeling of patella moving laterally as the patella relocates from a medial position into the trochlea.

Increased passive medial patellar translation with knee in full extension and 30° of flexion when compared to contralateral side.

The patient may experience pain and apprehension with a medially directed force on the lateral border of the patella, suggesting a positive medial apprehension test.²

Medial subluxation test according to Fulkerson: This is a provocative test in which the patella is pushed medially with the knee in extension and then released on abrupt knee flexion. Reproduction of patient’s symptoms with this maneuver suggests MPS.¹⁵

Gravity subluxation test¹⁶: The patient is positioned in the lateral decubitus position with the affected leg up. The leg is passively abducted, the knee extended, and quadriceps relaxed. In this position, gravity causes the patella to subluxate medially and out of the trochlea. A sulcus may appear at the site of previous lateral release. The test is positive for MPS when a voluntary contraction of the quadriceps does not center the patella into the trochlear groove and it indicates detachment of vastus lateralis tendon. In patients with hypermobility, the patella may subluxate medially because of joint laxity; however, with an active quadriceps contraction, the patella could be pulled back into the trochlea.

In cases of extensive LRR, the patella can translate laterally and rotate/tilt upward when pushed laterally— the lateral patellar float sign¹⁷ (Figure 11.4).

The involved knee is examined in the seated position. The examiner attempts to center the patella in the trochlea with a laterally directed force on the medial patella. This will usually provide immediate relief as the patient actively ranges the knee.¹⁷

“Reverse” McConnell taping can be performed to hold the patella laterally and prevent it from subluxating
medially. Significant relief of pain with taping would be a diagnostic test for MPS (Figure 11.5).

Similarly, application of “reverse” patellar stabilizing brace (Palumbo brace) with the buttress pad or strap on the medial side would minimize or eliminate symptoms of MPS, thus confirming the diagnosis.

Coronal and rotational plane alignment has to be evaluated in standing and prone position, respectively.

Gait analysis has shown abnormal medial patellar translation during swing phase when the leg is unloaded and when the quadriceps muscle is relaxed. This finding supports the importance of balance of passive structures around the patella and the reason for failure of muscular rehabilitation program to address MPS.¹⁸

Standing anteroposterior (AP) view, lateral view in 30° of knee flexion, and Merchant views should be obtained.

Radiographs should be measured for anatomic risk factors, including patella alta, trochlear dysplasia, sulcus angle, congruence angle, and lateral patellofemoral
angle. Radiographs should also be evaluated for any arthritic changes.

If standing alignment shows coronal plane malalignment (varus or valgus), then full-length standing radiographs of bilateral lower extremity should be obtained.

Rotational malalignment on clinical evaluation can be quantified by a computed tomography rotational profile scan.

Stress axial radiographs can document and quantify MPS objectively. A comparison with the contralateral asymptomatic side is more important than the absolute value of displacement. Teitge et al demonstrated that a 4 mm increase in medial or lateral excursion of patella of the symptomatic knee compared to asymptomatic knee was statistically significant for instability in the measured direction. Based on stress radiographs, patients could be divided into four groups: normal, lateral instability, medial instability (previous LRR), and multidirectional instability (previous LRR and lateral instability).¹⁹

Magnetic resonance imaging (MRI) should be evaluated for risk factors (such as tibial tubercle-trochlear groove distance and trochlear dysplasia), position of the patella, and status of the articular cartilage. Extent of previous lateral release and other patellar stabilization procedures are assessed to plan for treatment of MPS (Figure 11.6).

Kinematic MRI in various degrees of knee flexion can detect patellar maltracking that may be difficult to evaluate clinically. Of 43 knees with lateral release, kinematic MRI showed 10 (23%) had lateral subluxation of patella and 27 (63%) had MPS. Surprisingly, 17 of 40 patients (43%) also showed MPS on the contralateral asymptomatic knee.²⁰