Patellar Instability and Dislocation

Marc Darrow, MD, JD

When you are diagnosed with patellar instability, your doctors have concluded that your patella, or knee cap, shifts and moves out of the grove it sits in at the patellofemoral joint. This can be the result of an obvious and traumatic impact injury or degenerative wear and tear to the quadriceps tendon and the medial patellofemoral ligament (MPFL), patellomeniscal ligament, patellotibial ligament, and retinaculum, the major connective tissue that hold the knee cap in place. In degenerative conditions and post-traumatic injury pain, functional issues, and eventually osteoarthritis will develop.

The knee cap or patella dislocations is a common injury mostly seen in younger athletes, especially in the female adolescent athlete. It is also an injury that can often reoccur and why surgery may be recommended.

A February 2022 paper (1) looked to understand how to better predict the risk of patella dislocation recurrence following a first lateral patellar dislocation. The study team looked at patients with first lateral patellar dislocation and a minimum two-year follow-up after nonoperative conservative care treatment.

  • In total, 115 of 201 patients (57%) experienced recurrent lateral patellar dislocation within 2 years after the initial lateral patellar dislocation. Patients younger than sixteen at primary lateral patellar dislocation, history of contralateral instability, and trochlear dysplasia (a flattened knee groove that the patella sits in) were significant risk factors for recurrent lateral patellar dislocation. The prediction accuracy including these 3 risk factors was 79%. Conclusion: Young age and trochlear dysplasia are major risk factors for early recurrent lateral patellar dislocation.

Most patella dislocations will be treated with conservative care options.

Most patella dislocations will be treated with conservative care options. In case where the dislocations caused fragments of cartilage or extensive cartilage damage, surgery may be explored because of high recurrence rates. However surgery may not be the answer for all.

A February 2022 paper (2)  examined active duty military personnel who had patella stabilization surgery and assessed their long-term outcomes with their patellar stabilization surgeries. In this paper a retrospective review of a consecutive series of 63 patients who underwent operative management for patellar instability at a military medical center between 2003 and 2017.

All cases were performed by a single sports medicine fellowship-trained orthopaedic surgeon. Patients with recurrent lateral patellar instability whose nonoperative management failed were included. All patients underwent arthroscopic imbrication of the medial patellar retinaculum (loosening of the ligaments), an open lateral retinacular release (to get a tilted knee cap back in place), and an Elmslie-Trillat tibial tubercle osteotomy (bone was shaved down).

Outcome measures at final follow-up included recurrent instability, need for surgical revision, subjective assessments (did it help?), and military-specific metrics (were the military personnel able to resume their military functions).

  • A total of 51 patients were included (34 men, 17 women; average age 27 tears old).
    • Four patients (7.8%) reported redislocation events, and 4 underwent revision surgery.
    • Twenty-five patients (49.0%) reported a decrease in activity level as compared with preinjury, while 10 (19.6%) cited restrictions in activities of daily living.
    • Of the 21 patients remaining on active duty, 6 (28.6%) required an activity-limiting medical profile.
    • Of the 48 active duty patients, 12 (25.0%) underwent evaluation by a medical board for separation from the military.

As mentioned trochlear dysplasia is characterized by a shallow trochlear groove. Its is this groove that the knee cap slides up and down in. Problems with the trochlear groove is usually diagnosed as a congenital problem (you were born that way) or lateral patellar tracking (the dislocation or moving out of place of the knee cap is grinding down the bone).

Another cause we see in patients is the diagnosis of Hypermobile Ehlers-Danlos Syndrome (hEDS). A disease where the ligaments of the body are in state of laxity or looseness. Patients with hEDS may experience frequent dislocations and an ability to put the knee cap back in place by themselves.

Patellar Instability and Dislocation Treatment:

In many patients the initial knee dislocation will resolve on its own or can be put back in place by a medical professional without the need for surgery. For conservative care the patient may be prescribed or recommend NSAIDs anti-inflammatory medications, rest, compression sleeves and knee braces and physical therapy. Longer-term activity modification may also be required.

Physical therapy for Patellar Instability and Dislocation

A physical therapist will offer treatments to help stabilize the knee.

The key to physical therapy is range of motion. To get to increasing range of motion, pain must be dealt with. The physical therapist may recommend conservative care pain relief options such as regular ice treatments, knee braces and sleeves and activity modification.

Research on more reps with lighter resistance – Blood Flow Restriction Therapy for Patella Instability

A January 2022 paper (4) assessed the effectiveness of blood-flow restriction training for patellar instability. The researchers hypothesized that this strategy would improve patient-reported outcomes and accelerate restoration of symmetric strength and knee biomechanics necessary to safely return to activity. They write: “Patellar instability is a common and understudied condition that disproportionally affects athletes and military personnel. The rate of post-traumatic osteoarthritis that develops following a patellar dislocation can be up to 50% of individuals 5-15 years after injury. Conservative treatment is the standard of care for patellar instability however, there are no evidence-informed rehabilitation guidelines in the scientific literature. . .  The current standard of care for non-operative treatment of patellar instability is highly variable does not adequately address the mechanisms necessary to restore lower extremity function and protect the long-term health of articular cartilage following injury.” Blood-flow restriction training, less resistance higher level of reps under supervised care may be the answer.

Patella surgery

In some instances and as discussed above surgical treatment may be necessary when patella dislocation becomes chronic and degenerative wearing away of the bone is occurring.

Surgeries that may be recommended include:

  • Arthroscopic lateral-release. The ligaments that hold the knee cap in place are cut to relax their grip on the knee cap and allow it to resume its rightful place within the trochlear groove.
  • Medial patellofemoral ligament reconstruction. This surgery is typically reserved for complete or almost complete tear of the ligament. Typically grafts from the hamstring tendons are used in place of the ligament. This is a very major procedure.
  • Knee osteotomy (tibial tubercle transfer) is an open (non-arthroscopic) surgery that shaves down and remodels bone that seeks to reshape the knee in a more natural anatomy. This is a very major procedure.

Injections for Patellar Instability and Dislocation

The patella, as mentioned, sometimes just pops itself back into place. Sometimes it has to be put back into place. To manipulate the patella in place doctors will usually offer lidocaine as a painkiller and then manipulate the knee. On occasion, as reported in the medical literature, (3) giving lidocaine allows the patient to slowly bend their knee without pain and the patella slips back into place.

The Patella Tendon and Patella Instability

Degenerative wear and tear or overuse injury is a common problem in the knee tendons, among them the patellar tendon. The patellar tendon helps hold the knee cap in place as it attaches the bottom of the patella / kneecap to the top of the shinbone (tibia). Typically wear and tear of the patella tendon signifies a greater knee wear problem and patella and overall knee instability. Pain, weakness and instability can come from the quadricep muscles because the quadriceps tendon is stressed by patella maltracking, any injury or weakness to the connective tissue attachments of the patella can results not only in patellar instability, but degenerative breakdown of the patella cartilage or chondromalacia patella, unexplained knee pain as in patellar femoral syndrome, or patellar tendinitis, inflammation of the tendon.

1 Wierer G, Krabb N, Kaiser P, Ortmaier R, Schützenberger S, Schlumberger M, Hiller B, Ingruber F, Smekal V, Attal R, Seitlinger G. The Patellar Instability Probability Calculator: A Multivariate-Based Model to Predict the Individual Risk of Recurrent Lateral Patellar Dislocation. The American Journal of Sports Medicine. 2022 Jan 21:03635465211063176.
2 Zhou ML, Cruz CC, Johnson MZ, Bottoni CR. Outcomes of Patellar Stabilization Utilizing a Combined Arthroscopic and Open Technique: A Retrospective Review With 5-Year Follow-up. Orthopaedic Journal of Sports Medicine. 2022 Feb 24;10(2):23259671211068404.
3 Berry CA, Summers MA, Reddy KI. Superior Patellar Dislocation Reduced by Intra-articular Injection: A Case Report and Review of Literature. JBJS Case Connector. 2021 Apr 1;11(2):e20.
4 Brightwell BD, Stone A, Li X, Hardy P, Thompson K, Noehren B, Jacobs C. Blood flow Restriction training After patellar INStability (BRAINS Trial). Trials. 2022 Dec;23(1):1-8.



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