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M. DE BUTTET and G. PASQUIER
Roubaix
INTRODUCTION
Dislocation of a total hip replacement (THR) implanted through a posterior approach is known to occur at varying times from arthroplasty. It is, however, encountered frequently enough to make it a major concern.
It has been suggested that dislocation results from technical faults committed by the surgeon. However, it has been known to occur in technically perfect THRs, with correctly placed components. Thus, there must be other - in particular soft-tissue (gluteus medius) related - factors that are to blame.
Nowadays, the positioning of the implant components is always strictly checked; also, surgeons will resort to certain strategies at surgery, such as using augments or anti-dislocation cups, or suturing the external rotators; also, during rehabilitation, patients are instructed in how to use their hips to prevent them dislocating. While these measures have led to a drop in the dislocation rate after THR, what has been achieved is not yet sufficient.
One very efficient means of preventing dislocation is good capsular technique. By this we mean the preservation of capsular tissue during the incision; the protection of the capsule during dissection and the implantation of the device; and proper repair of the capsule at the end of the procedure.
ANATOMY
The capsule is a sleeve that extends from the acetabular margin to the base of the femoral neck and the medial border of the greater trochanter. Laterally, it reaches less far on the posterior aspect, stopping one third of the neck length away from the greater trochanter, than it does anteriorly, where it attaches to the intertrochanteric line. Behind, it is reinforced by the ischiofemoral ligament, which spirals obliquely behind the femoral neck and attaches in front of the digital fossa.
The capsule and its three ligaments (anterior, inferior, and posterior) spiral in the same direction. Twisting and untwisting, they tauten in extension and slacken in flexion. In addition, the ischiofemoral ligament and the superior portion of the capsule are tightened in adduction and internal rotation.
TECHNIQUE
Anything that needs to be done to the capsule is part of the general incision and wound closure technique. Patient positioning is not affected.
The approach is a posterolateral one, with the patient positioned on his or her side. The incision is taken through the gluteus maximus muscle, in the direction of its fibres. The short external rotators are identified, exposed, divided as close as possible to their insertions on the trochanter (care being taken not to open the capsule), tagged with sutures, and reflected backwards.
(1) Preservation of the capsule
The capsule is exposed by the gentle use of an elevator in the avascular plane that separates it from the external rotators. It is then incised, with a longitudinal incision following the midline of the femoral neck, and extending from the acetabular margin to the intertrochanteric line.
Through this incision, the acetabular labrum is identified and incised. Cutting the labrum will feel like cutting a meniscus.
As will be seen from the description given above, opening the capsule is straightforward. Using this technique, two flaps of equal size will be obtained, which should be taken on stout sutures.
With the capsule opened, and the labrum completely incised, dislocation of the hip is readily accomplished. The flaps are tensioned by the internal rotation of the hip, and will lie in front of the femoral head. In its inferior portion, the capsule is, however, adherent to the femoral neck, and will need to be detached until the lesser trochanter comes into sight. A spike retractor is placed under the lower border of the neck, reflecting the flap. The spike retracts against the acetabular notch (inside the joint). The usual landmarks are identified, and the femoral neck is resected using a saw of the surgeon's choice (oscillating or reciprocal).
Two traction sutures are placed, and a self-retaining retractor is inserted to hold the flaps out of the way. (The capsular tissue is strong enough to withstand the use of a retractor.) In this way, excellent exposure of the acetabulum is obtained. A spike retractor is inserted in the anterior column of the acetabulum to hold the upper end of the femur out of the way. The labrum may now be excised down to bone, without damaging the articular surface of the capsule. This excision of the labrum is straightforward and complete, giving excellent exposure of the entire bony margin of the acetabulum. If need be, the transverse acetabular ligament may be nicked, to permit the insertion of a lower spike retractor.
If required, exposure may be improved by taking the capsular detachment a little further. The exposure thus obtained matches that provided by capsulectomy. The acetabulum may now be prepared, and the cup implanted.
 Fig. 1 Joint capsule (posterior aspect) On the posterior aspect of the femoral neck, it is inserted on a line that marks the junction between the proximal two thirds and the distal one third of the neck. |
 Fig. 2 Joint capsule, ischiofemoral ligament, and line of incision. The ligament spirals behind the neck of the femur. Its femoral insertion is in front of the digital fossa. |
 Fig. 3 Capsular incision |
 Fig. 4 Repair of the capsule |
 Fig. 5 Repair of the capsule. As a rule, 4 or 5 sutures will suffice to close the capsulotomy. The capsule is not sutured to the femur. In some cases, the implant will be completely buried; more frequently, it will not. |
(2) Repair of the capsule
Once the implant has been reduced, the first stage in the closure of the incision is commenced. This stage is independent of the reinsertion of the short external rotators.
If the capsular flaps have been properly fashioned and adequately protected throughout the procedure, closure of the capsule should be straightforward.
The capsular tissue lends itself to suturing: It is strong; it can easily be taken on a needle; it is also pliable.
The suture is started with one stitch over the acetabular margin, at the end-point of the capsular division or detachment. An interrupted suture should be used, so as not to pucker the tissue. A stout absorbable braided suture (metric 5) is recommended.
The interrupted sutures are placed and tied one by one, working towards the intertrochanteric line. A total of four to five stitches should be enough to close the capsulotomy safely and effectively.
The upper flap is more difficult to take on a needle, since it is buried under gluteus medius. The problem may be overcome by internally rotating the hip, with the knot tightened in external rotation.
A drain is left in the joint, and the tissue layers are closed in customary fashion. The short external rotators are reattached, and the muscles and fascia closed in the usual way. The skin is closed over a second drain.
With this technique of capsulorrhaphy, no change will need to be made to the preferred protocol of postoperative management (removal of drains; early and rapid mobilization of the patients; resumption of partial or full weight-bearing).
Obviously, the patient will still need to be taught to avoid certain movements while the soft tissues are healing.
(3) Problems and pitfalls
During the detachment of the external rotators, the capsule may be damaged. This is not a major problem. The capsular incision will simply have to be taken through the damaged zone, even if that means finishing up with flaps of slightly different sizes.
Preserving the capsule does not, as a rule, interfere with the preparation of the femur after the resection of the femoral neck, nor with the insertion of the actual prosthesis. The main problem with exposure may be at the acetabulum.
As pointed out above, the two capsular flaps may be of different sizes. If so, they may interfere with exposure during the preparation of the acetabulum. Should this be the case, the capsule will need to be mobilized by taking the detachment a little further, behind the acetabular margin, using traction sutures and a retractor positioned in such a way as to hold the flaps out of the way.
This mobilization has the added advantage of showing exactly where the upper acetabular bony rim is. This information should make it possible to avoid placing the cup without adequate bony cover.
The two most difficult parts of the procedure are
(a) Choosing the orientation of the cup. The posterior bony landmarks will be partly
hidden; however, extra-articular guides may be used to great advantage.
(b) The placing of the PE insert, in cases where a cup with biological fixation is being used.
Posterior and inferior osteophytes may interfere with insertion, in which case these osteophytes should be resected flush with the metal ring, working from the posterior margin of the cup towards the transverse acetabular ligament. This procedure is performed inside the capsule, using a chisel. This obviates the risk of damaging the capsule.
Care should be taken to ensure that the insert is properly impacted into the cup.
The flaps may be damaged by the reamers, which may push the tissue into the cavity; also, the insertion of a threaded cup may cause the lower flap to be caught on and in the sharp threads. If the capsular tissue has been weakened in this way, suturing would be more difficult, and the suture itself less sound. Fortunately, the most important zone of the flaps - the one closest to the acetabular margin - is the least likely to suffer damage.
When the suture has been completed, the implant may be completely hidden. However, this would be the exception rather than the rule.
No sutures are inserted through the posterior border of the greater trochanter. This is why internal rotation is not restricted following this capsulorrhaphy.
STUDY MATERIAL
Between May 1989 and April 1995, a series of 360 consecutive primary total hip replacements was performed by the same surgeon, using a posterolateral approach.
The patients were being given a THR for osteoarthritis, fractures complicating osteoarthritis, or for avascular necrosis.
The implants used were :
(1) Femoral components: cemented - Muller self-locking; Protek PCS; cementless -
Landanger Corail(2) Cups: cemented - Muller; cementless - Arc 2F
(3) Heads: All the heads were 28 mm.
No cups with anti-dislocation hoods were used in this study.
Two groups were identified:-
Although the quality of the repair effected tended to vary somewhat, it was always possible to suture the capsule, in all the pathologies for which the patients were having THR.- a first group, operated on between May 1989 and March 1993, comprising 186 arthroplasties in whom the technique described in this article was not used.
In this group, there were 22 dislocations, three of which occurred more than two years after implantation; five recurred, requiring revision surgery.
- a second group, operated on between April 1993 and April 1995, comprising 174 patients, who routinely underwent capsular repair as described in this article.
Of the patients with osteoarthritis of the hip, none dislocated after THR; there was only one case who had a fleeting, non-recurrent episode of dislocation. He had an arthritic hip and had suffered a hip fracture; he was also in poor general condition, and had intellectual deficits.
CONCLUSION
At three years' follow-up, we feel that the technique described in this article is a useful means of preventing dislocation after THR from a posterior approach.
Technically, it requires an additional stage in the procedure, with meticulous dissection of the capsular tissues; however, it would appear to be feasible under all conditions; and once the surgeon has become versed in the technique, it should not add unduly to the overall complexity of THR.
The capsular technique proposed is straightforward to perform, which is why we would suggest that it be used wherever synovectomy is not required. One major advantage of this capsular repair is the reinforcement, by the non-stretchy and solid capsular tissue, of the inherently stretchy tissue of the short external rotators.
This technique, however, must be seen within the wider context of total hip replacement: Whilst it can help to improve results, it is not, in itself, a substitute for the careful preoperative planning and meticulous positioning of the implant components that will be crucial to the outcome of hip arthroplasty.