Abstract
There has been a reluctance, until relatively recently, to consider replacement of the hip in patients with substantial neuromuscular imbalance. This relates to many factors, including the young age of many (such as cerebral palsy in the older teen and young adult), developmental anatomic abnormality, oft-present poor bone health, neuromuscular imbalance, and the risk of complication; especially dislocation. Mental retardation also introduces challenges with rehabilitation and an increased burden on the family and societal support systems if the outcome is to be maximised. With the development of newer techniques and technology, and the emergence of encouraging outcome studies, these patients can be more easily offered predictable relief of pain, a reasonable chance of improved function, longevity of the reconstruction, and an acceptable risk of complication.
A large number of background neurological diagnoses can lead to hip degeneration, or can introduce increased complexity during management of hip degeneration unrelated to that background. Be that as it may, a short list of fundamental questions is common to all and will help guide management:
Important questions to be addressed include:
1. Did the NV imbalance precede skeletal development? This relates to the dependence of skeletal shape and size on the loads being placed upon it: hence “Form Follows Function”. The shape and size of the hip, and location of the femoral head, will be much different in the young adult with spastic dislocation due to cerebral palsy, when compared with the elderly adult with a late onset CVA-related spasticity superimposed on hip degeneration.
2. Is the muscle tone which will support the hip arthroplasty predominantly spastic or flaccid? In each there is a risk of dislocation, which needs to be addressed at the index procedure, but in spasticity there is the added question as to what tissues need to be released or de-functioned so as to alter the magnitude and direction of the joint reaction forces.
3. Is pain the main reason for consultation? Because pain relief is the most predictable outcome that we can offer, it should guide the indications and timing of intervention. Replacement of the NM hip to improve function, in the absence of pain, should be approached with great caution.
