Bipartite patella is a congenital condition (present at birth) that occurs when the patella (kneecap) is made of two bones (instead of a single bone). Normally, the two bones would fuse together as the child grows. But in patella bipartite, they remain as two separate bones.
Most of the time, this condition is silent. The person doesn’t even know he or she has it. But direct trauma to the kneecap or repetitive injury (overuse) can trigger painful symptoms. In this article, orthopedic surgeons from Canada review the classification, clinical features, and diagnosis of bipartite patella. They offer treatment alternatives for symptomatic cases.
Bipartite patella can be classified or labeled according to the location of the bone fragments. This is determined using imaging studies such as X-rays, MRIs, and scintigraphy (bone scans). In Type I, the extra bone is at the bottom of the patella. This area is referred to as the inferior pole.
Type II tells us the fragment is along the lateral edge. Lateral refers to the side of the patella away from the other knee. And a Type III bipartite patella has a fragment at the upper-outer corner of the patella. This area is called the superolateral pole.
Treatment is usually nonoperative at first. Rest, activity modification, and sports restriction are advised. Anti-inflammatory medication is usually prescribed. Physical therapy is started to stretch and strengthen the muscles surrounding the knee.
Severe pain may require immobilization and/or steroid injections. Putting the knee in a brace with limited knee extension prevents contraction of the quadriceps muscle. The result is to decrease a traction force on the fragment.
In most cases, conservative care is carried out for at least six months before considering surgery. There are some exceptions. For example, immediate surgery may be needed in cases of direct trauma or when the pain prevents daily activities. When surgery is recommended, there are several possible methods to choose from.
The first is an open incision and removal of the bone fragment. There are many studies using this method and reporting good-to-excellent responses. The procedure is invasive. The surgeon cuts down to the quadriceps tendon. Removing a large fragment this way can cause problems later with the patellofemoral joint. This is where the patella moves up and down over the femur. The two surfaces no longer match up for smooth tracking.
The second surgical treatment is a lateral retinacular release. The surgeon cuts the connective tissue holding the quadriceps to the outer edge of the kneecap. This releases the traction force put on the patella by the vastus lateralis muscle. The vastus lateralis is the outer most tendon of the four tendons that make up the quadriceps muscle.
In some cases, a lateral release allows the two bone fragments to join together and heal. Pain is relieved within four weeks. Athletes are able to return to their pre-injury level of sports participation. This procedure can be done arthroscopically, thus avoiding an open incision. Studies show that results are improved with this technique. There is less swelling after surgery and faster recovery of muscle strength post-operatively.
A third surgical technique is the subperiosteal detachment of the vastus lateralis insertion. This method accomplishes the same thing as a lateral release but without weakening the vastus lateralis muscle. By just releasing the tendon from the fragment and from under the first layer of bone, the action of the muscle is not altered. The fragment may or may not be removed. This depends on how severe the condition is. In some patients, the fragment can and does join with the rest of the patella.
And finally, there is a more invasive approach, called open reduction and internal fixation (ORIF). An open incision is made. The fragment is attached to the main patella with wires or screws. This procedure is used when the fragment is large and removing it would cause patellofemoral arthritis later.