August 10, 2006
There are two ways to look at approaches to hip resurfacing or any hip arthroplasty. One is to view it with the amount of muscle damage done. The other is to view it in respect to the blood supply or the vascularity. The post approach is traditionally known as the muscle sparing approach and the anterior and anterolateral approaches are the muscle compromising approaches. These approaches are known as Hardinge approach or London hospital approach. There are many more modifications of this with slight variations but essentially they are the same and they disturb muscles to varying extents. The muscle here refers to the Abductor group or the muscles which lift your leg sideways and is the most important muscle of the hip. The post approach spares this completely. Interestingly there is now an anterior approach which is getting to be very popular for mini -THR and this is known as the mini Watson Jones approach or the micro hip approach. This does not disturb the abductor though it a ant. approach. However resurfacing cannot be done through this approach. Even when one does a THR the head has to be sawed off in place and then delivered out separately. Or in other words the hip cannot be ‘dislocated’ through this approach which precludes hip resurfacing. However some muscle have to be cut in any approach to get access to the hip and in the post approach, one cuts the short ext rotators which are flimsy , small muscles in the back of the hip. These are stitched back. These muscles are relatively unimportant. It is largely accepted that the post approach is more conducive to early and complete return of function as it is muscle sparing. The ant approaches which disturb the gluteus medius will result in slower and incomplete return of function depending on the amount of muscle disturbed and the intactness of the muscle repair over long term. The younger and the more active the patient , the more would be the perceptible difference between the ant and post. approaches as regards function. Thus an elderly patient having a THR will appear to have the same result with either approach whereas a young patient having a resurfacing will have an obvious difference.Michael Freeman , an English surgeon established in 1978, the fact that the blood supply in an osteoarthritic hip is different from a normal hip. In full blown arthritis the blood supply to a large extent changes to inside bone( intra-0sseus) from a pattern that is predominantly outside bone (extra osseus ).Therefore in osteoarthritis , any approach can be attempted without a risk to the blood supply. Hence in osteoarthritis, as the blood supply issue is taken out of the equation only the muscle damage is relevant and therefore post approach is better. In fact when Derek McMinn developed modern resurfacing , he first attempted it through the anterior approach and found so much of muscle damage that he decided to change to posterior. However in non-OA indications like AVN , the situation is little different and the intra-osseus blood supply is not well developed. Increasingly it is becoming increasingly obvious that neck capsule preservation is vital in these non-OA indications. Hence we have developed the neck capsule preserving ( NCP ) approach where the end arteries to the neck and head -neck junction has to be preserved. We have been doing the NCP approach for the last 6 yrs in predominantly non-oA indications with excellent results. Neck capsule preservation is not possible through the anterior approach and therefore the post approach is more suited for non-OA indications. The other benefit of the NCP approach is the fact the capsule is also repaired back completely so that the surgeon can confidently advise patients that there wont be any restrictions post-op. The repaired capsule will prevent the patient from doing any awkward movement even inadvertently. This is very useful in the first 6 weeks which is the time taken for a pseudo capsule to form when the surgeon does not stitch back the capsule . Therefore capsule repair is of relevance only in the 1st 6 weeks The 3rd issue comes into play when a femoral component of a resurfacing is done uncemented. This is the situation where one has to be extraordinarily careful as even a little necrosis of the head bone would cause failure of the implant. When one uses cement, the cement converts the head into a ‘composite’ of live bone, dead bone and cement. Some bone unviablility is easily tolerated due to the presence of cement. Therefore in uncemented femoral resurfacing one has to use the Ganz approach or surgical dislocation where the blood> supply should preserved entirely. Although this appears to be desirable in theory for all resurfacing it has its own problems. It involves a trochanteric osteotomy and reattachment with screws. The pt has to be partial weight bearing for 6-8 weeks till the ostetomy unites. Prof Ganz from Berne developed this approach for non arthritic hips for pts in their 20s to treat femoral acetabular impingement (FAI). These patients have a completely normal pattern of blood supply (completely exta-osseus) and in spite of this, pts do not develop any problems. This technique is described as surgical dislocation and surgeons employ this for any condition that requires a dislocation of a normal ( non-arthritic) hips. The surgical dislocation is always done posteriorly. Thus 3 different situations with regard to resurfacing need 3 different approaches and all of them are posterior! Anterior or posterior refers to which side the hip is dislocated and not on where the incision would be. Irrespective of whether anterior or posterior approach is done , the incision will always be on the side ( exactly lateral). So one cannot deduce approach employed by looking at the incision. Therefore the skin incision is same for both approaches.
Vijay Bose. consultant orthopaedic surgeon Chennaiwww.hipresurfacingindia.com