The technique of enlarging the acetabulum by means of an extra-articular bony extension goes back to Koenig (1891), and was first described in the literature by Marcel Lance [1], in 1925. The shelf consists of a corticocancellous autograft that is fitted on the anterosuperior aspect of the joint capsule in order to provide a larger weightbearing surface and, thus, to reduce the pressure on the cartilage. In the 60s of the last century, a number of authors (among them Castaing, Salmon, Judet, Roy-Camille, Rieunau, Chiari, and Spitzy [2]) devised modifications of the original technique, in order to improve graft placement and graft fixation. In these modified techniques, the surgical approach initially suggested by Lance – an incision similar to the Smith-Petersen approach – was retained. This route involves wide exposure of the iliac crest. We felt that a less invasive approach would be beneficial, in that it would make for easier surgery and postoperative management [3]; also, a simpler procedure would allow more patients to be selected for this operation.

Some patients with osteoarthritis (OA) of the hip are perhaps not immediate candidates for total hip arthroplasty (THR), since their radiographs show the OA to be at a comparatively early stage; the hip may be painful, but has a full ROM; and the patient is still relatively young. In such patients, minimal-access surgery, with a short in-patient stay, no change to the bony structures, and little need for rehabilitation, would be considered a success if it could postpone the need for THR by ten years. Even if the procedure fails, it would not be too upsetting for the patient, since a THR could be performed under optimal conditions. There is, thus, an excellent risk-benefit ratio.
The case discussed below serves to show the minimal-access techniques that can be used, with special reference to the shelf procedure.

Fig. 1: This 46-year-old lady, a pharmaceutical company representative, had OA of the left hip, without total loss of joint space; the femoral head had collapsed above a large subchondral cyst. OA was secondary to hip dysplasia, with a positive Wiberg angle and a slightly excessive inclination of the acetabular roof. The femoral neck is in valgus and anteverted; Shenton’s line is not interrupted. MRI confirms that the subchondral cysts have been caused by OA, and shows an anterosuperior peripheral longitudinal tear of the labrum. A CT scan clearly shows the subchondral bone lesion above the cyst.

- The patient had had hip pain for the past two years; for the last six months, the pain had been permanent and refractory to analgesics. The patient’s walking distance was five blocks. THR would undoubtedly have been an effective solution. However, the implant would in all probability have needed to be revised when the patient was older. A femoral valgus osteotomy might have made things worse, given the collapse over the subchondral cyst and the absence of an osteophyte in the lower part of the femoral head. A femoral varus osteotomy would have led to shortening and deformation of the proximal femur, and made subsequent THR that much more difficult. Pelvic osteotomy is major and difficult surgery, which, in a patient at this lady’s age and stage of OA, would have been unlikely to be beneficial.

Fig. 2: The patient is positioned on a fracture table, with the hip in flexion and internal rotation; 20 kg of traction is applied. The external landmarks (ASIS, greater trochanter) are marked out on the skin [4–6].

Fig. 3: The joint is distended with saline, and the hip is distracted.

- The patient was offered hip arthroscopy in the first instance, in order to determine the condition of the cartilage and of the labrum. If this initial investigation showed that conditions were suitable, a minimal-access shelf procedure would be done under the same anaesthetic; core decompression with filling of the subchondral cyst with a cancellous autograft from the trochanteric region would also be performed.

Fig. 4: The femoral head cartilage is healthy overall. The acetabular cartilage shows Grade II and Grade IIIA articular surface damage. The anteriorly detached labrum is trapped between the head and the acetabulum.	Fig. 5: After disimpaction of the labrum, Grade IV articular surface damage (exposed bone) is seen at the acetabular site formerly hidden by the labral fragment.	Fig. 6: There is clear evidence of the collapse of the subchondral bone in the femoral head.
Fig. 7: An osteocartilaginous loose body is found adhering to the synovial membrane in the fossa.	Fig. 8: The loose body is detached with forceps.	Fig. 9: The loose body is aspirated via the outflow cannula.
Fig. 10: The trapped labral fragment is debrided with a holmium YAG laser.

- The arthroscopic stage of the procedure was completed in 45 minutes; in the light of the findings, it was decided to continue and perform a shelf through a minimal access. The patient’s position on the orthopaedic table did not need to be changed; however, traction was slightly decreased, to lower the capsule and create a space for the shelf.

Fig. 11: First, the graft is harvested. A 4-cm incision is made, starting 2 cm behind the ASIS.	Fig. 12: The incision is deepened to the superior cortex of the iliac wing. The internal and external cortices are exposed. In this zone, the iliac wing is thick.	Fig. 13: The graft measures 3 cm x 3 cm. For smaller subjects, or in mild dysplasia, a narrower (2.5-cm or 2.0-cm) graft may be used.
Fig. 14: The anterior and posterior cuts are kept parallel to each other.	Fig. 15: The inferior cut is angled about 45°, from lateral to medial.	Fig. 16: The resultant graft is corticocancellous; it has three cortices. The 3-cm x 3-cm defect in the iliac crest may be left unfilled, or filled with a bone substitute.
Fig. 17: The inferior cut is trimmed with a saw...	Fig. 18: ... to produce a 45-degree bevel, with the cancellous bone sandwiched between two cortices.	Fig. 19: Fixation will be by means of a cannulated 7.2-mm screw, of the type commonly used to stabilize femoral neck fractures. The drill-guide pin is introduced at right angles to a line passing through the bevel of the graft. The pin must be directed at right angles, to ensure complete graft/ilium contact, following fixation.
Fig. 20: The graft is drilled, with the drill guided by the pin...	Fig. 21: ... and tapped.	Fig. 22: A 6-cm-long screw of 7.2-mm diameter, with a long thread is inserted; a washer is used to protect the superior cortex of the graft.
Fig. 23: The graft is ready for insertion.	Fig. 24: A stab incision is made half-way along a transverse line drawn from the tip of the greater trochanter to a vertical line passing through the ASIS. This is the usual hip arthroscopy portal site. The tensor fasciae latae is split in the direction of the fibres as far as the capsule, using forceps so as not to damage an accessory branch of the lateral cutaneous nerve of the thigh. The guide pin is introduced.	Fig. 25: With image intensifier monitoring, the tip of the guide pin is brought against the lateral border of the iliac wing, at a site 5 mm above the joint space and 2 cm behind the AIIS (found be probing with the pin). Next, the pin is directed 45° cephalad, in the coronal plane. Only the near cortex is perforated, with the tip of the pin left resting against the inside of the opposite cortex.
Fig. 26:The skin incision is enlarged on either side of the pin entry site, over a total length of 4–5 cm. This incision parallels the one over the iliac crest.	Fig. 27: The fibres of the tensor fasciae latae are dissociated on either side of the pin. One spike retractor is placed anteriorly against the AIIS, and another spike posteriorly, against the posterosuperior portion of the acetabular rim. In this patient, the posterior spike has been replaced by a Steinmann pin.	Fig. 28: At this stage, the reflected head of the rectus femoris must be detached, since it would come between the hip bone and the shelf.
Fig. 29: The correctly placed guide pin will go through the reflected head. The tendon is divided anteriorly and posteriorly, or divided posteriorly and reflected forward. The distance between the guide pin and the tip of the anterior retractor will be ca. 1.5 cm.	Fig. 30: The hip bone is freshened on either side of the pin, using a tissue grasper/rongeur.	Fig. 31: ... or with a chisel. The object is to freshen the bone, without going through the cortex, since doing so might interfere with screw stability.
Fig. 32: The drill is introduced, guided by the pin.	Fig. 33: Both cortices are drilled, care being taken to ensure that the guide pin does not penetrate into the pelvis. If the pin is angled 45° cephalad, it would only go into the psoas and the obturator internus. The iliac vessels course more caudad, which is why a guide pin directed at right angles to the hipbone would put these vessels at risk. The two iliac wing cortices are tapped.	Fig. 34: The graft with the inserted screw is guided by the pin. The retractors must be carefully positioned, to prevent the entrapment of muscle tissue between the graft and its host site.
Fig. 35: Graft rotation is controlled with vulsellum forceps, while the screw is being tightened.	Fig. 36: The screw is tightened until the shelf is against the hipbone. The threaded portion must be entirely within the iliac wing. A washer must be used, to prevent splitting of the graft. The screw must be tightened sufficiently, to prevent graft instability and non-union.

The shelf was completed in 35 minutes.

- In a third step, core decompression and grafting of the subchondral cyst was performed. The procedure was similar to the techniques used in the management of femoral head necrosis [7].

Fig. 37: A 1-cm-long incision is made over the femur, at a site 3 cm below the crest.	Fig. 38: The soft tissues are pulled apart. A 4.5-mm hole is drilled in line with the axis of the femoral neck, at the point where the lateral cortex begins to thicken. This drill hole is over-reamed with a 10-mm reamer.	Fig. 39: The 8-mm trephine is advanced into the cancellous bone up to the subchondral cyst.
Fig. 40: Advancement of the trephine is checked with biplanar fluoroscopy.	Fig. 41: The 4.2-mm drill is passed through the cyst to the level of the subchondral bone.	Fig. 42: The drill hole is over-reamed with an 8-mm reamer. The trephine is reintroduced up to the cyst, and gradually advanced by hand, to push up the subchondral bone. Throughout this part of the procedure, the hip remains slighlty distracted.
Fig. 43: The trephine is drawn back 2 cm. The obturator/graft pusher is inserted. The tube will contain an 8-cm-long plug of 6-mm diameter.	Fig. 44: A check is made to ensure that the trephine is at the entrance to the cyst.	Fig. 45: The trephine shaft is held by its handle, while the obturator/graft pusher is tapped.
Fig. 46: The graft introduced into the cyst is tamped with the trephine.	Fig. 47: Postoperative management is straightforward: 48 hours’ in-patient stay; mobilization on Day 1; ambulation with partial (50% of BW) weight-bearing protected with elbow crutches for three months; no rehabilitation; patient discharged home.	Fig. 48: At three months, the patient is walking without aids. This patient had no pain, and could walk unlimited distances.
Fig. 49: Good scar cosmesis.	Fig. 50: The shelf does not cause anterior impingement, provided that it is not too wide, and that there is no structural abnormality such as femoral neck anteversion and acetabular insufficiency. Prior to surgery, a check should be made to ensure that the patient has full internal rotation in flexion.
Fig. 51: At 2 years, the patient was walking without a limp; the shelf was well integrated; the joint space still preserved; the subchondral cyst in the femoral head filled; and the hip pain-free with a good ROM.

Our series
To date, we have been able to follow up 32 patients, for a period of more than two years (range: 26 to 40 months). The mean in-patient stay was three days (range: one day to five days). All the patients started weight-bearing on the first postoperative day. None of the patients went to a rehabilitation facility. Partial weight-bearing with crutches was for a mean of 48 days (range: 29 to 75 days).

Pain
One patient was lost to follow-up. Twenty-four patients had a completely painless hip, and no limitations to their activities. Five patients had a Harris Hip Score (HHS) better than 80; two patients had an HHS of between 70 and 75. Two patients had severe pain, and required THR.

Union
Thirty-one shelves united, with radiographic evidence of callus at a mean of three months. One case of non-union, with early graft fracture, was due to the non-use of a washer, and subsidence of the screw in the graft. The patient concerned was lost to follow-up.

Complications
None of the patients suffered paralysis of the lateral cutaneous nerve of the thigh, haematoma, or deep-vein thrombosis. Four patients had moderately severe donor-site pain, which remitted within four months. Six patients had pain at the screw site, and had the screw removed after the eighth month from surgery.

DISCUSSION

Under this heading, we will look at the advantages and the disadvantages of the technique, before considering its indications.

Advantages

Simple, reliable technique

- The incision is in the safe zone as described in the context of hip arthroscopy [4–6]. Hip arthroscopy has a very low complication rate; such complications as do occur are due to the use of an orthopaedic table.

- The principle of a corticocancellous shelf fixed with a screw is a somewhat novel one. However, the technique resembles that devised by Latarjet [8] for use in the shoulder. While the glenohumeral joint is inherently less stable than the hip joint, and although the screw used in the shoulder does not have the same purchase as the 7.2-mm screw than can be used in the ilium, the rate of non-union and of necrosis at the shoulder site has been low. Our technique is not too dissimilar to the screw-fixed shelf proposed by Castaing [9]. The concave aspect of the graft snugs itself against the convex shape of the extra-articular surface of the capsule. The compressive forces along the axis of the screw are transmitted by the three cortices of the shelf. The cancellous surface in contact with the freshened iliac wing is comparatively large, thanks to the bevel given to the graft. This promotes graft stability and healing. The surrounding muscles contribute to the overall integration of the graft. The outcome of the first 16 shelves performed by us suggests that the graft is rapidly integrated. (The only failure encountered was due to a technical error: the screw had been inserted without a washer, and the screw head subsided into the graft.)

- There is little risk of injury to nerves or vessels inside the lesser pelvis. The guide pin pierces only one cortex; its tip is lodged in the opposite cortex. The pin is angled at 45°, which eliminates any danger to the iliac vessels, since, in case of inadvertent perforation of the inner table, the tip would merely finish up in the bulk of the iliopsoas. If the pin were to be introduced at right angles to the iliac wing, its penetration into the lesser pelvis might result in injury to an artery or a vein, since, at the pelvic inlet, the iliac vessels course medial to the cranial portion of the acetabulum.

- The use of an image intensifier when positioning the shelf allows the surgeon to find the correct level. While there is nothing in the literature concerning the rates of shelf malpositioning associated with the different techniques, shelves are often found on postoperative radiographs to be positioned too high, even though the procedure had been performed open. With the traditional incision, the error is due to insufficient dissection of the reflected tendon of the rectus femoris.

- Inserting the shelf through a minimal access is, obviously, a much less aggressive procedure than is a Chiari shelf or a triple innominate osteotomy, and the postoperative course of the minimal-access procedure is also more straightforward. Some patients would, however, be candidates for any one of the three operations [2]. The minimal-access technique is mastered much more rapidly.

Easier postoperative management

- Since the technique involves little muscle dissection at the donor and the recipient site, there will be less postoperative pain and less intraoperative blood loss. This means that transfusion will not be required, and patients can be discharged earlier.

Resumption of weight-bearing, and return home

- The force of the proximal muscles in the lower limb is undiminished following the procedure. The ROM is unaffected by surgery. The patients do not need to go to a rehabilitation facility.

- From weight-bearing radiographs in single-leg stance, we have seen that, in dysplastic hips, the femoral head tends to recentre itself with a slight lateral offset. This recentring is due to the force exerted by the capsule, which twists and presses against the labrum in extension. (In dysplastic hips, th labrum is frequently found to be hypertrophied.) Recentring is also due to the orientation of the resultant of the muscle forces [6].

EAt surgery, we have found that mobilizing the hip does not produce excessive stress on the graft, even if the joint is flexed to 90°, provided that the recommended graft dimensions have been observed. Also, the screw has been found to have an excellent purchase. The 45-degree bevel ensures intimate apposition of the lower edge of the graft, and buttresses the graft to enhance its resistance to upward-directed forces.

It follows that the shelf is not excessively stressed by the femoral head, during weight-bearing, since the minimal-access procedure has little if any adverse effect on the active and passive hip stabilizers. In the light of these findings, we decided to allow our patients to resume partial weight-bearing on the first postoperative day.

Morbidity

Acetabular augmentation by means of a shelf is an established technique. When performed through a conventional incision, it has a low morbidity.

- The rate of infections reported in the literature is less than 1%; non-union, without any major clinical repercussions, has been observed in 7% of the cases. However, the reported rate of damage to the lateral femoral cutaneous nerve is high at 17% [9, 10]. The use of a minimal-access technique should not adversely affect the infection and non-union rates of the shelf procedure. However, as regards lateral femoral cutaneous nerve lesions, the minimal-access technique appears to be superior: we have not observed any complications of this kind, either in the shelf series or in the hip arthroscopy procedures, which use a similar approach. Follow-up to date is too short for any conclusions to be drawn with regard to shelf osteolysis in the long term.

- For as long as computerized navigation systems are not universally available, the use of an image intensifier remains mandatory; however, exposure times are short. Fluoroscopic monitoring must be performed during the short time when the pin is being introduced. Also, the screw fixation of the shelf must be observed with fluoroscopy, to check that proper compression is being obtained. The mean exposure time thus required is about one minute.

- In slender subjects, the screw may give rise to anterior muscle pain. We have had to remove three screws, at between eight and twelve months from surgery.

- In a dysplastic hip with anterior-column aplasia and anteversion of the femoral neck, internal rotation will be excessive. A well-placed shelf of reasonable size will not produce an anterior cam effect in flexion/internal rotation. All our patients retained internal rotation >= 10°.

Indications

- The long-term outcomes of shelf augmentation surgery are well known. They show that the ideal candidate for this procedure is a young patient, with a moderately dysplastic hip that is painful but not associated with an radiological signs of OA; also, the hip remains correctly centred in monopodal stance. The 16-year rates of survival without the need for THR in such hips have been reported to be between 80 and 87% [9, 11, 12].

- According to the literature, radiological improvement of the joint space has also been seen in more advanced (Stage III or IV) OA managed with a shelf; in particular, 16-year rates of survival without the need for THR in such patients have been found to be of the order of 60% [13, 14]. Our simplified technique allows the range of candidates to be widened, to include patients in their forties or fifties, with a painful hip as a result of OA secondary to dysplasia. With our minimal-access technique, more than 50 per cent of the patients should be able to gain at least ten years before the need for THR arises. Also, hip replacement following a previous shelf procedure should be technically straightforward, providing that any anterior cam effect is abolished; and should we well accepted by a properly informed patient. Good scar cosmesis, a short in-patient stay, and the prospect of being reasonably independent at home without any rehabilitation programme, are arguments that make this surgery attractive to the patient. The use of a minimal access for the shelf procedure does not rule out any of the customary incisions at revision. Since the proximal end of the femur will not have been deformed, primary arthroplasty with a standard anatomical stem remains an option

References

1. Lance, M., Constitution d’une butée ostéoplastique dans les luxations et sub-luxations congénitales de la hanche. Presse médicale,, 1925. 33: p. 922-31. 2. Chiari, K., [History and present indications for corrective surgery of the acetabulum in hip dysplasia (author's transl)]. Arch Orthop Unfallchir, 1976. 86(1): p. 67-76. 3. Chiron, P., et al., Technique de la butée de hanche percutanée. Rev. Chir. Orthop., 1999. 85 (supplement 3): p. 102-103. 4. Chiron, P., Technique de l'arthroscopie de hanche. Maîtrise Orthopédique, 1994. n° 30 (janvier 1994): p. 1-10. 5. Chiron, P., et al., Voies d'abord de l'arthroscopie de hanche. rev. chir. orthop., 1994. 80 supplement 1: p. 170. 6. Chiron, P., Technique et indications de l'arthroscopie de hanche. Cahiers d'enseignement de la SOFCOT. Conférences d'enseignement 2001., 2001. 78: p. 33-50. 7. Chiron, P., Le point sur le traitement chirurgical des ostéonécroses de la tête fémorale. Maîtrise orhtopédique., 2001. n° 105 (Juin Juillet 2001): p. 12-17. 8.Allain, J., D. Goutallier, and C. Glorion, Long-term results of the Latarjet procedure for the treatment of anterior instability of the shoulder. J Bone Joint Surg Am, 1998. 80(6): p. 841-52. 9. Amsallem, G., La butée ostéoplastique de hanche. Étude rétrospective d'une série de 88 interventions avec un recul minimum de 16 ans. Thèse Méd., Orléans-Tours,, 1989. 10. Hamanishi, C., S. Tanaka, and T. Yamamuro, The Spitzy shelf operation for the dysplastic hip. Retrospective 10 (5- 25) year study of 124 cases. Acta Orthop Scand, 1992. 63(3): p. 273-7. 11. Migaud, H., et al., [Outcome of hip shelf arthroplasty in adults after a minimum of 15 years of follow-up. Long term results and analysis of failures of 56 dysplastic hips]. Rev Chir Orthop Reparatrice Appar Mot, 1995. 81(8): p. 716-23. 12. Judet, J., Résultats des butées cotyloïdiennes avant 10 ans au plus de recul (Symposium de la SOFCOT). Rev. Chir. Orthop., 1976. 62: p. 511-577. 13. Migaud, H., et al., Butée arthroplastique de hanche. Etude statistique des facteurs radiographiques pronostiques. A propos de 94 cas revus avec 14 ans de recul. Rev. Chir. Orthop., 1994. 80 supplement 1: p. 177. 14. Laurent, M., et al., [Radiological improvement following isolated tectoplasty on advanced secondary osteoarthritis of the hip]. Rev Chir Orthop Reparatrice Appar Mot, 1993. 79(6): p. 484-91.

Maîtrise Orthopédique N° 123 – April 2003