Jay C. Albright
DEFINITION
Instability of the patellofemoral joint is a significant cause of pain and dysfunction in children and young adults.
Instability or dislocations may occur in either ligamentously lax individuals or in athletic non-lax individuals.
Instability or dislocation patients without generalized ligamentous laxity are more likely to sustain an injury to the ligament and to structures about the knee.
Injuries sustained to the medial aspect of the patellofemoral joint may lead to ligament disruption of the medial patellofemoral ligament with or without stretching or tearing of the medial retinaculum. This may lead to persistent pain or recurrent instability of the patellofemoral joint.
The key to treatment is the persistent complaint of instability feelings and examination consistent with instability with or without pain.
Care must be taken to avoid realignment surgery for pain only.
ANATOMY
The medial restraints of the patellofemoral joint are made up predominantly of the medial retinaculum and the medial patellofemoral ligament. Forty to 60% of the resistance to lateral translation is supplied by the medial patellofemoral ligament.3
The medial patellofemoral ligament is about 15 mm wide. It extends from the medial aspect of the patella, about 10 to 15 mm distal to the superior pole of the patella, near the widest portion of the patella, to the medial epicondylar area just above the origin of the medial collateral ligament.
This area can also be located distal to the vastus medialis obliquus (VMO) insertion into the quadriceps tendon and anterior to the medial intermuscular septum.
The lateral retinaculum may also be tight, characterized by less than 12 mm of medial translation.2
The bony anatomy and alignment of the lower extremities must also be considered. The quadriceps angle may be greater than average, increasing the lateral translational force.
So-called miserable malalignment syndrome may exist, including excessive femoral anteversion with or without increased external tibial torsion.1,2
PATHOGENESIS
The onset of patellofemoral instability or dislocation can be either traumatic or atraumatic. In young athletes, it can occur during a valgus twisting maneuver such as swinging a baseball bat while twisting out of the way of a pitch. It may also occur with a direct blow on the valgus bent knee.
Like an anterior cruciate ligament injury, it is common to hear or feel a “pop.” If the patella completely dislocates, the athlete may be found to have a deformity of the knee and may be unable to actively extend the knee.
It may be associated with significant swelling or little swelling. It is commonly difficult to distinguish between a medial collateral ligament tear, a meniscal tear, or an acute patellofemoral subluxation or dislocation.
The bony anatomy of the patellofemoral joint may also be abnormal with a deficient lateral femoral slope of the trochlear groove, leading to decreased force needed to laterally translate or dislocate the patella.
NATURAL HISTORY
Patients with an atraumatic presentation of instability or dislocation of the patellofemoral joint have a higher likelihood of repeat instability episodes despite aggressive physical therapy and bracing.1,2
Patients with a traumatic-onset presentation may have a fracture or loose body created by the subluxation or dislocation. If a loose body exists, as in other conditions, surgical intervention is warranted.
There is controversy over whether to acutely operate on first-time dislocators who are young athletes without generalized ligamentous laxity.
PATIENT HISTORY AND PHYSICAL FINDINGS
The clinician must evaluate potential associated or confounding injuries and consider the differential diagnosis, which should include (but not be limited to) meniscal tears, which are characterized by joint-line tenderness, painful popping with provocative maneuvers (full squat, McMurray, or Apley compression test), and with or without loss of full extension.
A thorough examination will include the following:
Examination for effusion
Patellar stability testing. Instability of 25% to 50% indicates increased laxity but a still-competent retinaculum and medial patellofemoral ligament. Instability of more than 50% indicates insufficiency of both structures.
Femoral rotation: Average rotation is external rotation greater than or equal to internal motion.
Tibial alignment: Average axis is 10 to 15 degrees of external tibial torsion.
The clinician should observe and palpate the patella for lateral subluxation (J sign) during active range of motion.
IMAGING AND OTHER DIAGNOSTIC STUDIES
Anteroposterior (AP), lateral, and Merchant views are all standard and provide information regarding the acute injury.
Each radiograph is evaluated for fracture or loose fragment necessitating more emergent surgical indications.
DIFFERENTIAL DIAGNOSIS
Meniscal tear
Medial collateral ligament tear
Chondral injury or bruise
Anterior cruciate ligament tear
Tendinitis
Sindig-Larsen-Johanssen disease
NONOPERATIVE MANAGEMENT
Over 80% of patients will respond well to nonoperative treatment.
Nonoperative treatment is appropriate for multiple dislocators or subluxators, especially those who have generalized ligamentous laxity or an atraumatic type of presentation.
Controversy exists as to the best treatment of first-time dislocators who are ligamentously tight, with or without a traumatic (but usually forceful) event.
First-time dislocators who are young athletes without ligamentous laxity or a loose body or fracture are the most likely to respond well to nonoperative treatment.
Some advocate early surgical intervention to repair the medial patellofemoral ligament and medial retinaculum even without fractures or loose body.
Nonoperative regimen for a dislocation includes:
Rest, ice, compression, and elevation, plus anti-inflammatory medications
Immobilization for about 6 weeks
Immediate physical therapy to strengthen the weakened quadriceps and a patellar protection program
Bracing, with a lateral patellar restraint type of brace, for return to activity
Treatment options for recurrent subluxation should include.
Bracing with a lateral patellar restraint type of brace
Physical therapy: a patellar protection program emphasizing strengthening of the hip flexors, abductors (which are routinely weak in this patient population), and quadriceps in particular
The clinician should emphasize to the patient that therapy requires participation at home as well as at therapy sessions.
SURGICAL MANAGEMENT
Operative intervention should not be considered in chronic subluxators unless they prove that despite good effort in therapy over 6 to 12 months, instability still is problematic.
The surgeon should be wary of operative treatment for patients with pain without instability.
Recurrent dislocators who dislocate in a brace during physical activity despite good effort during therapy and training as well as those who dislocate during activities of daily living in a brace after therapy are candidates for surgical intervention.
Any loose body or patellar avulsion fractures with large displaced fragments are indications for early surgical intervention.
Preoperative Planning
All imaging studies are reviewed for other pathology that also needs to be addressed concurrently.
Before positioning, an examination of the knee under anesthesia (including ligamentous testing) should be performed.
The examination should include a Lachman test, pivot shift, varus–valgus stress test, and anterior–posterior drawer as well as medial and lateral patellar stability testing at 45 degrees of knee flexion. Results should be compared with those from the opposite knee.
Translation of the patella over 50% of the width of the patella laterally indicates an incompetency of the medial patellofemoral ligament and the medial retinaculum, and both should be addressed at surgery (FIG 1).
FIG 1 • Complete dislocation of the patella at the time of surgery.
Positioning
The supine position is used with the patient's operative leg free and with a tourniquet on the proximal leg.
The foot of the table is flexed about 30 to 45 degrees and a lateral post is used for valgus moment, visualizing the medial compartment.
The opposite leg can be positioned per the surgeon's preference, depending on whether the foot of the table is flexed 90 degrees or if the foot is kept flat with a lateral post.
Approach
If an arthroscopic lateral release is being performed, a 4- to 5-cm limited medial approach may be used, centering on the widest portion of the patella (FIG 2). Subcutaneous flaps can be elevated to allow great mobility of the prepatellar skin to limit the size of the incision.
Alternatively, an open subcutaneous lateral release can be performed through a 1-cm incision, along with the medial plication–imbrication, or both may be done through a midline incision.
FIG 2 • First, arthroscopic examination and limited lateral release (black line) are performed. The surgical incision is centered over the medial aspect of the widest portion of the patella.
TECHNIQUES
MEDIAL RETINACULAR PLICATION (MODIFIED INSALL)
After dissection of the subcutaneous tissues, a medial parapatellar incision is made, leaving about 2 mm of tendon with the VMO (TECH FIG 1A).
This incision in the tendon and the retinaculum is made from about 3 to 4 cm above the superior pole of the patella distally to 3 to 4 cm distal to the inferior pole of the patella medial to the tendon, leaving enough retinaculum with the tendon to suture to.
The entire depth of the tendon and retinaculum is incised.
The knee is then held in 45 degrees of flexion and the patella is held in position in the center of the trochlea (TECH FIG 1B).
Three nonabsorbable no. 1 or no. 2 sutures are placed but not tied in a horizontal mattress fashion.
These are typically placed 25% to 40% across the width of the patella from medial to lateral, imbricating the edge of the tendon of the VMO and the retinaculum distally and laterally.
With the three sutures held tight, the knee is placed through a range of motion, from full extension to 90 degrees of flexion, to check that enough imbrication has been performed.
The sutures are then tied and a 0 absorbable suture is used above and below the imbrication to reinforce the tension set by these sutures.
A running 0 absorbable suture then can be sutured over the imbrication to help reinforce the imbrication as well as lower its profile.
The wound is irrigated and closed in layers.
Absorbable 3-0 or 4-0 monofilament should be used in the skin.1,2
TECH FIG 1 • A. Medial parapatellar incision is made with 2 to 3 mm of quadriceps tendon left attached to the vastus medialis obliquus. B. The knee is placed at 45 degrees of flexion, with the patella centered in the femoral groove; set the tension of the medial side by imbricating the medial retinaculum.
MEDIAL PATELLOFEMORAL LIGAMENT RECONSTRUCTION
The incision in the quadriceps mechanism and retinaculum is kept as extrasynovial as possible, especially directly medial to the patella and distally.
The retinaculum is dissected from the subcutaneous tissue superficially back to the medial intermuscular septum (TECH FIG 2A).
It is then dissected from the synovium deep back to the intermuscular septum.
A puncture hole is made in the retinaculum immediately anterior to the intermuscular septum, superficial to the medial epicondylar insertion of the natural ligament and immediately distal to the VMO.
The distance from the widest portion of the patella to the planned puncture site is measured.
The medial 6 to 8 mm of full-thickness quadriceps tendon is taken typically as a 50- to 60-mm-long graft remaining attached to the superior pole of the patella (TECH FIG 2B).
The graft is subperiosteally reflected distally about 10 to 12 mm from the superior pole of the patella (more distally laterally than medially, to allow it to fold over on itself during fixation and tensioning).
A nonabsorbable suture is placed in the free end of the graft, with a whipstitch or other graft stitch performed with two ends.
The graft is then passed deep to the retinaculum through the puncture hole to the superficial side of the retinaculum (TECH FIG 2C).
The tension is then set via the medial retinacular suture plication as described above before setting the tension of the graft.
At 45 degrees of knee flexion the graft is then tensioned to allow no more than 25% lateral translation of the patella at 45 degrees of knee flexion (TECH FIG 2D).
The graft is secured into position with no. 1 or 2 nonabsorbable suture placed through the medial intermuscular septum periosteum of the medial epicondyle and the graft and retinaculum at the puncture hole in the retinaculum.
It is further secured by 0 absorbable sutures in the graft and retinaculum, catching the graft superficial and deep to the retinaculum as the free end of the graft is directed back toward the patella.
The suture in the free end of the graft is also used to secure it into position.
Once the graft is secured and imbrication is complete, the knee is flexed to 90 degrees to ensure that no over-tightening of the quadriceps mechanism has occurred and that the sutures stay in place.
Tracking of the patella is also checked as described above.4
TECH FIG 2 • A. The surgeon dissects deep to the medial retinaculum, posterior to the medial epicondyle and the medial intermuscular septum. B. If the medial patellofemoral ligament is to be reconstructed, the surgeon measures the length of graft needed. A full-thickness quadriceps tendon graft 6 to 8 mm wide is obtained, with attachment to the patella maintained at its widest portion. C. The medial retinaculum is punctured at the point marked by placement anterior to the intermuscular septum, distal to the vastus medialis obliquus, and superficial to the medial epicondyle. D. The graft is tensioned and secured to the medial retinaculum–intermuscular septum, also at 45 degrees.
POSTOPERATIVE CARE
Patients are placed in a hinged postoperative knee brace locked in full extension.
Physical therapy for range of motion (passive and active assisted) should be started in the first few days to combat arthrofibrosis.
Weight bearing is protected with crutches until the patient is comfortable enough to walk in a locked knee brace in full extension.
During the initial phase of therapy, patellar mobilization, quadriceps activation, straight-leg raises, pain modalities, and edema control are important.
Range of motion is restricted to 0 to 90 degrees for the first 3 to 4 weeks postoperatively.
At 4 weeks, full range of motion is allowed, with progressive quadriceps strengthening, edema control, and pain control, and gait training is initiated.
Brace use in community settings is continued until adequate quadriceps strength has returned (about 6 weeks).
From 6 to 12 weeks, there is continued progression of quadriceps strengthening.
Functional return to activities starts at 3 months postoperatively.
COMPLICATIONS
Failure of fixation is typically seen at the time of surgery if knee is tested from 0 to 90 degrees.
Late fixation failure is uncommon but can happen if flexion beyond 90 degrees is started too soon postoperatively.
Arthrofibrosis should be treated aggressively with manipulation under anesthesia if greater than 90 degrees of flexion is not obtained by 6 weeks.
Continued pain may occur, especially if not enough or too aggressive of a lateral release was performed, leading to either increased pressure on the patella or medial pressure and instability.
Injury to the cutaneous nerves is common, and patients should be warned of this risk. It can be avoided with well-placed small incisions.
Recurrent instability may occur in patients with rotational or angular malalignments that either are not recognized or cannot be addressed because of skeletal immaturity.
REFERENCES
1. Insall JN. Disorders of the patella. In Insall JN, ed. Surgery of the knee. New York: Churchill Livingstone, 1984:191.
2. Insall JN, Bullough PG, Burstein AH. Proximal “tube” realignment of the patella for chondromalacia patellae. Clin Orthop Relat Res 1979;144:63–69.
3. Mountney J, Senavongse W, Amis AA, et al. Tensile strength of the medial patellofemoral ligament before and after repair or reconstruction. J Bone Joint Surg Br 2005;87B:36–40.
4. Noyes FR, Albright JC. Reconstruction of the medial patellofemoral ligament with autologous quadriceps tendon. Arthroscopy 2006;22:904.e1–7.