Patellar dislocation

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Original Editors - Jeremy Luytens as part of the Vrije Universiteit Brussel's Evidence-based Practice project

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Definition/Description

A luxating patella or patellar dislocation is a severe acute injury where there is a shift of the patella. Because of this shift the patella will leave the patellofemoral groove.

It is important to make a differentiation between acute primary patellar dislocation, which accounts for 2-3%, and habitual dislocation for recommendations with varying treatment approaches. Primary (first-time) patellar dislocation is defined as a clinical entity that usually causes a traumatic disruption of the previously uninjured medial peripatellar structures [14,15,16].
One of the common findings related to acute, primary, traumatic patellar dislocations is hemarthrosis (bleeding into joint spaces) of the knee, caused by rupture of the medial restraints of the patella. [13]

Clinically Relevant Anatomy

The patellofemoral joint is the portion of the knee joint between the patella and the femoral condyles. The patellofemoral articulation totally depends on the function of the quadriceps. It increases the angle of pull of the patellar tendon, improving the mechanical advantage of the quadriceps in knee extension.

The articular surfaces consist of the patella and the trochlear surface of the femoral condyles. The articular cartilage on the medial facet is thicker than on the lateral facet, with the lateral facet bigger than the medial.

The femoral condyles only project slightly in front of the shaft of the femur but project quite a distance posteriorly. The anterior aspects of both condyles are included in the articular area of the patella. The patellar articular surface is larger on the lateral femoral condyle than on the medial. There is an anterior projection on the lateral femoral condyle lateral to the patellar groove. This is the bony factor, which prevents lateral dislocation of the patella. The trochlea is on the anterior, distal end of the femur. The groove is continuous posteriorly with the intercondylar notch of the femur. The lateral facet is more prominent and has a greater radius.

The suspension and movement of the patella is provided by passive and active stabilizers.
• Passive: fascia lata, ligamentum patellae, capsule of the knee, ligamentum patellofemorale medial and lateral and ligamentum meniscopatellare medial and lateral
• Active: the four heads of the quadriceps, ligamentum patellae and the retinacullum

Epidemiology /Etiology

Athletics are often associated with patellar dislocation ( Ficat ’77, Hugston ’84 ). It is most common in females in the second decade of life.

Patellar dislocation most often result results from a non-contact injury to the knee. But apart from the traumatic component, it is also important to refer to the presence of predisposing morphological and functional patellofemoral disorders. Dominant predisposing factors need less trauma for dislocations, and vice versa. It’s etiology is regarder as multi-factorial, being associated with: reduced osseous constraint form the lateral femoral condyle; an imbalance between stronger lateral tissues, such as the lateral retinacullum and vastus lateralis, which are able to overcome weaker medial structures, especially the medial patellofemoral ligament and the distal vastus medialis; and finally biomechanical issues such as femoral and tibial rotation, and pes planus.

The typical mechanism of injury is a twist of the leg, with the femur rotating internally on a fixed foot and tibia. Valgus stress is often associated with this rotating mechanism, thereby creating a strong laterally directed force, dislocating the patella ( Hugston ’84 ). A direct blow as well to the lateral side of the knee, producing a valgus stress, as to the medial side of the knee producing a direct dislocating force can also create this injury ( Fu ’90 ).

A knee tape with a lateral reinforcement will reduce the movement of the patella so that can be used as prevention.

The patient will experience pain, instability of the knee and blocking of the knee after the trauma. After de dislocation there will be a swelling on the medial side of knee because on this side a lot of tissue will be hit.

Differential Diagnosis

A radiography to exclude osteochondral fractures and avulsion fractures, patellar apprehension test is also needed, where the patella will provide resistance,Patella tracking assessment .

Research shows knee-specific scales yielded higher reliability coefficients and stronger validity than did general health instruments in Assessing Acute Patellar Dislocation. The Fulkerson and Lysholm scales were the only instruments to differentiate between patients with and without recurrent subluxations/dislocations. [34]
MRI is necessary to examine if the tendon is partially torn, for a complete tear a lateral X-ray might be sufficient due luxation of the patella. [17]

Diagnostic Procedures

A patellar dislocation can be diagnosed by using a MRI, conventional X-rays and computed tomography scans for measurement of the tuberositas tibiae-trochlea groove distance. [18]

Outcome Measures

An increase in the Q-angle could lead to lateral patellar dislocation or increased lateral patellofemoral contact pressures. A Q-angle decrease may not shift the patella medially, but could increase the medial tibiofemoral contact pressure by increasing the varus orientation. (35)

It is measured by drawing a line from the anterosuperior iliac spine to the centre of the patella, and a second line from the centre of the tibial tubercle to the centre of the patella. The angle where these lines intersect is regarded as the Q-angle. Traditionally, the Q-angle has been measured with subjects in supine, knee extended and with the quadriceps muscle relaxed. This is regarded as the ‘traditional’ or ‘conventional’ method of assessing Q-angle. (36)

In women, the Q angle should be less than 22 degrees. In men, the Q angle should be less than 18 degree. A typical Q angle is 12 degrees for men and 17 degrees for women. (37)

Examination

This is recommended to determine whether there are predisposing factors for dislocation, such as Patella alta, genu recurvatum, increased 'Q' Angle and patellar hypermobility

Medical Management

Immediately after the trauma there is an immobilization in a cylinder cast for 6 weeks and medication, supplements like glucosamine and NSAID’s that could be used to keep the knee strong. If required arthroscopy with or without retinacular repair, surgical repair of the torn retinacullum or immediate patellar realignment.

Acute primary dislocations can be managed conservatively by immobilisation with a removable knee brace, posterior splint, a cylinder cast or by surgical treatment. [30]

A posterior splint might be the best therapeutic option because of the low redislocation rates and knee joint restrictions. However, this recommendation is based on only one small study with significant limitations. Further investigation with modern braces and standardisation of immobilisation time is needed to find the most appropriate conservative treatment for patellar luxation.

Contemporary treatment regimens range from immediate mobilization without a brace to cast immobilization in extension for 6 weeks. In a patient who finds 6 weeks of immobilization unacceptable, a 3-week period of immobilization may be performed with the understanding that a higher redislocation rate may result. A 3-fold higher risk of redislocation was reported in those treated with immediate mobilization. [40]

Physical Therapy Management

An important thing is the important task of the physiotherapist: Prevention. The physiotherapist has to increase the functions after an injury, but he also has to prevent re-dislocation (in this way). He will give some advice and exercises.

Conservative treatment have included:
• Manual Therapy: Knee and Knee Mobilizations to improve the ROM of the knee
• Combination Therapy
• Strengthening exercises for quadriceps, hamstrings, adductors, muscles of the hip and lower abdomen. Important, is the use of closed kinetic chain exercises because of a greater number of advantages over the other forms of exercise.
• Stretching and flexibility training for hamstrings and quadriceps
• Proprioceptive exercises to improve the stability of the knee

Bracing and re-education can play an important role in the treatment and prevention of patellar dislocation.

Other than preferences for nonoperative treatment of primary patellar dislocations have been shown in previous studies [20,21,22], patients with habitual dislocations and patellofemoral symptoms seem to be benefited from reconstructive surgery [23,24].

Non-operative treatment:

Conservative treatment is still the most common treatment after primary dislocation of the patella. [25]
There is no statistically significant difference (p=0.091) between operatively and conservatively treated groups with regard to functional results. The same statistical outcome emerged when comparing incidences of re-dislocation (p=0.854), or other major patellar instabilities (p=0.856), between the groups. [26].
The results obtained should not promote a non-operative method on the basis of lower risk, but do support an individual approach based on precise diagnosis and defined criteria. [26].

Studies have shown taping resulted in a significantly better Lysholm score at 6 and 12 weeks post-dislocation (P=0.05), and also after 5-year follow-up (P=0.01). Knee function was better at 1-year follow-up. There were no cases of recurrent dislocation. [27]. 1B

Tape bandage immobilization seems superior to a cylinder cast even after 5 years. [27].

Surgical treatment:

Surgical intervention for first-time traumatic patellar dislocation is indicated in the following situations:
1) evidence on imaging or clinical examination of osteochondral fracture or major chondral injury;
2) palpable or MRI findings of substantial disruption of the MPFL (medial patellofemoral ligament)-VMO (vastus medialis obliquus)-adductor mechanism;
3) a patella laterally subluxated on the plain Mercer-Merchant view with normal alignment on the contralateral knee;
4) a patient fails to improve with nonoperative management especially in the presence of one or more predisposing factors to patellar dislocation;
5) subsequent redislocation [28]. Surgical stabilization significantly reduced the redislocation rate of primary traumatic patellar dislocation in a young adult population than those without surgical treatment, which was addressed in a prospective, randomized, controlled study [29].

For surgical treatment, There are several surgical options that may be used to prevent patellar dislocation and subluxation. These procedures may be used alone or in a combination:
- Lateral release
- Medial patellofemoral ligament (MPFL) reconstruction / proximal realignment
- Distal realignment / anteromedialization (AMZ)

Lateral release

Release of tight lateral retinaculum (soft tissue) to allow patella to track more medially. This procedure is sometimes performed alone on patients with mild instability of the patella.

Medial patellofemoral ligament (MPFL) reconstruction

A tightening of the MPFL or a reconstruction of this ligament can be used to balance the tracking of the patella to more natural (medial) alignment. This procedure is performed in patients with more severe patellar instability. A lateral release often is performed in conjunction with this procedure. (38)
After research 93% had good/exellent results using the Fulkerson’s functional knee score: Radiographic evaluation showed significant improvements in the congruence angle by an average of 20° (P= .0006), and in the lateral patellofemoral angle by an average of 10° (P = .0003). [32]

Conclusion: initial acute patellofemoral dislocations should be treated with immobilization and rehabilitation, as a majority of patients will do well without surgery. MRI is necessary to assess for osteochondral lesions, because they are associated with a poor prognosis if they are not addressed.

Distal realignment / anteromedialization (AMZ)

This realignment procedure involves transferring the tibial tubercle (where the patellar tendon attaches to the tibia). The bony attachment of the tendon is moved more medially to allow the patella to track normally. This procedure is performed on patients with severe patellar instability and is used in conjunction with the lateral release and/or the MPFL reconstruction.

Following the operation you will be taken to the recovery room for observation. Once the effects of the anesthesia have worn off and your pain is under control you will be released. Initial treatment after surgery consists of pain management, physical therapy and cryotherapy (ice). (38)

Key Research

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