The early diagnosis and treatment of developmental patella infera syndrome.

Noyes FR, Wojtys EM, and Marshall MT. Clin Orthop Rel Res 265:241-252, 1991.

This is the editor's interpretation of a paper published in the orthopaedic literature in 1991 - our attempt to make relevant medical articles accessible to lay readers. If you wish to read the original it is easy to ask your librarian to obtain a reprint for you from any medical library.

This paper distinguishes between -

  • developmental patella infera - where the patella is moving down into a lower position due to adhesions and scarring, but which situation is still potentially reversible.

  • permanent patella infera - where the situation is effectively irreversible, and salvage procedures can only try to improve the mechanics, not restore them.

It introduces the concept of using serial lateral (from the side) X-rays at 60 degrees of knee flexion to detect and monitor the situation of the patella in high risk cases.

Using a control group of 51 patients with minor knee problems and no prior surgical procedure on the knee nor any period of immobilisation, the authors established in their population the normal range of vertical height of the patella above the tibial plateau. They also compared the two knees of each patient as well as the reliability of serial measurements in the same patient.

They found, using three different measurement methods, that there was essentially no difference in the patellar height ratios between right and left knees (only 11-15%), but there was a large variation in the ratios from one individual to another.

Having established this baseline, they followed a series of five patients who had developed patella infera during the rehabilitation period or within six months, and whose patellar height ratio was decreased by at least 11-15%. The authors felt that in all cases they were still in the transient ('developmental') stage and that the patella infera was still amenable to surgical restoration.

They went on to detail the five case histories which make very interesting reading:

They found that adaptive shortening of the patellar tendon may occur within a very short period of time if the transient stage was not recognised and treated immediately. Numerous physical signs were present which should have alerted the clinicians to the development of developmental patella infera -

  • pain with quadriceps contraction
  • inability to perform a strong quads contraction within 2-3 weeks after injury or surgery
  • soft tissue swelling and oedema (tissue puffiness) around the patella
  • decreased patellar mobility from side-to-side and up-and-down (due to contractures in the soft tissues around and below the patella)
  • decreased tension in the patellar tendon when palpated, with failure of the patella to move upwards with a quadriceps muscle contraction
  • the patella on the affected side positioned lower (more 'distal') than on the unaffected side
  • warmth and tenderness to palpation around the patella, patellar tendon and fat pad
  • limited ROM (from contractures around the joint and outside of the joint) and joint effusion (fluid in the joint space)

They drew attention to the need to distinguish this from the syndrome of reflex sympathetic dystrophy (which is a syndrome where excessive pain, out of proportion to the findings, is association with other signs and symptoms due to nervous system changes - funny feelings in the skin, funny coloured blotches etcetera)..

The authors found that in the early development of patella infera the vertical height ratios between the two knees may differ by only a few millimetres. A difference greater than 15% may be considered abnormal. A second X-ray needs to be taken a week or two later to measure any further descent of the patella. The ratio must be compared to the opposite knee or a pre operative X-ray.

The key message is that patients with developing arthrofibrosis and early patella infera may often avoid surgey by participating in a closely supervised rehabilitation programme:

  • For soft tissue contracture around patella and fat pad - Start serial lateral X-rays to follow patellar height. Frequently test and evaluate patellar mobility. Teach the patient and helper patellar mobilisation techniques. If contracture remains, and the patella is descending - progress to early surgical release of the soft tissues.

  • For persistently weak quads - Start serial lateral X-rays to follow patellar height. Insist on palpable voluntary quads contractions within 24-48 hours after injury or surgery. Teach quads sitting isometric exercises. Get the patient to feel and assess quads tone, quads strength of contraction and patellar glide. Treat knee pain and joint effusion early. Use electrical muscle stimulation if necessary. Avoid immobilisation and promote early functional motion.

  • For disruption of extensor mechanism function (eg quads adhesions or femoral fracture) - Start serial lateral X-rays to follow patellar height. Insist on immediate mobilisation when possible after internal fixation. Insist on early quads function.