The patellofemoral joint of the knee is composed of the patella (kneecap) and femoral trochlea (trochlear groove). There is a wide range of normal patella positions and groove depths. The patella acts as a pulley, connecting the strong quadriceps muscle in the thigh to the tibia and allowing for knee extension. Because of the large forces going through the patella, it has the thickest cartilage of any area in the body. The patella runs within the trochlear groove as the knee begins to bend, and in most individuals, this engagement starts to occur at about 30 degrees of knee flexion. Until the patella engages in the bony trochlear groove the soft tissue stabilizing structures keep the patella from dislocating. The most important soft tissue patella stabilizing structure is the medial patellofemoral ligament (MPFL). This ligament can tear or stretch when the patella dislocates. The muscular structures, particularly the quadriceps, around the knee also play an important role in dynamic stability of the patella. Some variations to the normal anatomy can predispose people to patella instability. These may include a shallow groove, dysplasia (malformed) of the groove, alterations in knee alignment, a high-riding patella, and ligamentous laxity.
Patella dislocations are most commonly caused by a sporting injury in predominantly younger patients. Other injury mechanisms such as simple falls and work-place injuries can also cause a first time dislocation. For patients with recurrent (more than one) patella instability, simple daily events like getting up from a chair can even cause an instability event.
A patella dislocation appears as a dramatic change to the appearance of the knee, with the patella sitting off the lateral (outside) side of the knee. After the patella is reduced, patients typically will be able to bear weight through the knee, but will have extensive swelling and pain. It is common for swelling to last for a few weeks and for patients to lose some range of motion. For patients with chronic patella instability, the typical symptoms are apprehension with sporting activities, weakness, and pain at the front and side of the knee. Sometimes the kneecap feels like its “jumping” or shifting.
A thorough physical exam will note your strength, ligament stability, swelling, and range of motion. Some specific tests will also determine how the patella is tracking within the groove. X-rays are important to assess the bony anatomy and to determine if there is any dysplasia within the knee. We oftentimes will also order an MRI scan to determine if there is any cartilage damage and to look for tearing of the MPFL.
The most common injury associated with patella instability is cartilage damage on the patella or femur. In rare instances, particularly with more violent traumas, we also see other injuries such as ACL and meniscus tears.
For most patients with a first-time patella dislocation, a brief period of rest followed by physical therapy and a graduated exercise program will be all that is necessary. The risk of recurrence (it happening again) can be determined based on a multitude of factors (such as your age, activity level, ligamentous laxity, anatomic parameters, etc.). If the risk of recurrence is very high and/or we are dealing with recurrent instability, surgical management is indicated. For selected high-risk patients with a first time dislocation a patella stabilizing procedure may be best for the long-term health of the knee.
Certain exercises and therapeutic strategies can help build up dynamic stability around the knee. Particularly working on core, hip, and leg muscles is beneficial for patients with patella instability. After a dislocation event, therapies aimed at reducing inflammation
A patella stabilizing brace and/or taping can provide some stability to the patella. This can also provide an external cue to limit certain risky knee positions. The power of bracing is much less than the stability imparted by the bony and ligamentous structures inside of the knee.
MPFL reconstruction – The mainstay of patella stabilization surgery involves reconstructing the medial patellofemoral ligament (MPFL). This surgery reestablishes the tether between the patella and femur with a soft tissue graft. A MPFL reconstruction reliably reduces recurrent patella dislocations to around 5%, though certain patients may also benefit from bony realignment procedures.
Tibial Tubercle Osteotomy (TTO) – The tibial tubercle is the prominent area of bone where the patella tendon inserts. This procedure moves the tibial tubercle by cutting the bone and then securing it in a slightly different location to improve the patella tracking. This is typically done if the patella tracks too laterally (increased TT-TG >15mm) or if it rides too high (patella alta). Sometimes this procedure is recommended to protect the patella or trochlear cartilage with a cartilage restoration procedure. Patients are non-weight bearing for 4-6 weeks after a tibial tubercle osteotomy.
Trochleoplasty – When the trochlear groove is malformed the patella might track poorly and/or lack engagement. In severe cases, and in those patients who have failed previous stabilization procedures, the trochlear groove is re-shaped. I recreate the proper groove depth and remove any spurs. A MPFL reconstruction is also routinely performed so that both the bony and soft tissue stability is recreated. Learn more here.
Cartilage Restoration – Full thickness cartilage defects within the patellofemoral joint can benefit from cartilage restoration procedures.
Return to Activity: Return to full sporting participation can take some time after surgery and will be determined by the type of surgery you have. Patients will go through different phases in their rehab. The first goal is to minimize inflammation, promote healing, and regain mobility within the first month. We then have you regain strength and neuromuscular control of the knee. We then begin to incorporate running and impact around the 3-month mark. Finally, you will progress towards sports specific training and return to play between 4-6 months after surgery.
Dr. Daniel Elkin is a leading Orthopedic Surgeon performing Patella Stabilization Surgery in the Willamette Valley. He specializes in complex knee reconstruction and knee arthroscopy and is conveniently located in Salem, Oregon