Irish Journal of Orthopaedic Surgery and Trauma

ANALYSIS OF DALL MILES CABLE GRIP SYSTEM IN TROCHANTERIC FIXATION OF PRIMARY TOTAL HIP ARTHROPLASTY

Dept.of Orthopaedics,
Tullamore General Hospital,
Tullamore, Co.Offaly
Republic of Ireland

The use of trochanteric osteotomy for total hip arthroplasty continues to be debated. Many centres nowadays reserve the use of trochanteric osteotomy for the technically difficult and revision cases. Charnley(2) introduced the concept of "routine" trochanteric osteotomy in total hip arthroplasty, which he believed converted the operation to a true hip "reconstruction".

The advantages of trochanteric osteotomy are chiefly in providing excellent exposure, preservation of anatomical integrity of abductor muscles, greater stability against dislocation and restoration of biomechanical equilibrum. It gives an oppurtunity to influence favourably the ratio of body versus abductor moment arms. It allows for bony reconstruction and changes in leg length while retaining stability.(1,2,4)

Most problems are related to the techniques of trochanteric osteotomy and fixation. The major complication is of permanent impairment of abductor mechanism, usually due to non union of the trochanter. A variety of consequences have been attributed to nonunion, including impaired abduction strength, diminished walking endurance, limp, pain and an increased risk of dislocation. Other complications include broken or migrating wires, trochanteric bursitis and ectopic bone formation.(2,4)

There has been a significant decrease in complication rates of trochanteric osteotomies. This reflects greater appreciation of the factors contributing to non-union and development of better surgical techniques(4). One of the technical advances has been the use of Dall-Miles cable grip system for fixation of the osteotomised trochanter.

There have been varying results reported with the use of D.M.Cables since their introduction in 1983.The non union rates range from 2% to 38% and cable breakage seen in 3% to 33% (9,10). Fraying and fragmentation of cables has been described ,as well as metal debris and bone destruction around calcar and trochanter. (10)

The purpose of this study was to evaluate our early results with the use of "routine" trochanteric osteotomy in primary hip arthroplasty and fixation with the D.M.cable grip system.

We did a retrospective review of 96 patients, who had undergone a primary hip arthroplasty with trochanteric osteotomy fixation with D.M cable grip system. The patients selected were those with a minimum follow up of six months. The exclusion criteria were dementia or immobility .Each patient’s records were reviewed and they were contacted on the phone and called for review in out-patients.

In the clinic, patients were assessed using the Harris hip score and asked specifically for trochanteric problems. The examination included gait observation, Trendelburg test and clinical examination of the hip. Fresh radiographs were taken on the visit.

The Harris hip scores were compared to the pre-op scores filled in at the time of admission. The radiological grading (see table1)of trochanteric osteotomy (7)was done, comparing the immediate post –op radiographs to the recent radiographs.

The statistical analysis employed independent student t testing and unpaired chi squared testing for significance using SPSS software.

A total of 105 consecutive patients done by the senior author over a two and a half year period, were contacted for follow up out of which 96 patients turned up for out patient evaluation.2 patients had both hips done, making up a total of 98 hips . The mean follow up was 10.5 months after operation, ranging from 6 months to 28 months. The average age was 71.4 years and there were 49 male and 47 female patients.

The indications for surgery was Osteoarthritis (95%) Rheumatoid arthritis(3%) and avascular necrosis(2%).

The evaluation of the Harris hip score, showed an improvement in the average score from 25.3 pre-operative(range5 to 41) to 76.7 points(range 54 to 95)at last follow up. This is significant statistically (p<0.01).

The radiological grading (7)(see table 1) of trochanteric position showed that 89 patients (90.8%) had perfect apposition and union (Grade 1) and 2 of these patients had a single broken cable(fig.3), not affecting union. Eight patients(8.1%) had slight positional loss(1-3 cm) with union(Grade2).

There was one patient(1.2%) with non-union requiring re-operation(Grade 4). This 72 year old gentleman had a dislocation of the hip six months post –operatively (fig.4). It was felt that the major factor contributing to the dislocation was non-union with complete avulsion of the trochanter. This was treated with reduction of the hip and re-fixation of the trochanter using cancellous screws (fig.5). The patient was kept in a abduction brace for three months post-operatively . At six month follow up, his trochanter has re-united and he has not had any further dislocations.

There were 8 patients with general complications which included one superfical infection which responded to paraentral antibiotics. In terms of trochanteric problems 6 patients had persisting pain in the trochanteric region ,2 of these were treated by local anaesthetic infiltration. The trochanteric problems were unrelated to the radiological grading.

It was seen that 17 patients had a positive trendelburg sign at six month follow up. These patients were reviewed again after six months and 80% had improved. There was no statistical difference between the trendelburg positive patients and the rest, in terms of radiological grading.

*Author,year*	*Operations* *(hips)*	*Nonunion %*	*% cable breakage*
Dall and Miles 1983	321	1.5	3.1
Ritter 1991	40	37.5	32.5
Turner 1992	251	2	8
Silverton 1996	68	25	22
Menon1998	50	10	6
McCarthy 1999	320	9	10
Present series	98	1.2	3

Charnley believed that the trochanteric osteotomy was an essential part of the operation of total hip arthroplasty. He wrote "I still believe that study of methods of reattachment of the trochanter is the key to the future of total hip replacement."(2,4)

The reported incidence of trochanteric non-union varies widely. The earlier reports Volz and Brown in 1979 cited an incidence of 10 to18%(4). More recent reports show significant decreases in the rates to 0 to 3% in primary procedures (4).Amstutz and colleagues reported incidence of 2.3%. Ritter et al reported rate of 12.5% comparable to their revision rates(9). The lowest published rates are those of Jenson and Harris, of 1% in primary surgery(725 procedures)(5). This reflects better appreciation of the factors contributing to non union as well as better surgical techniques.

Charnley emphasised the need to stabilise the trochanter not only against cephalad migration but also against the anterior pull exerted by the abductors when the hip is in flexion. Failure to do so results in cyclic anterior posterior shearing forces with subsequent migration of the trochanter and failure of fixation devices(1,2,4). Significant resistance to anterior shearing forces is achieved by maximizing surface contact and interlocking of apposed cancellous surfaces on either side of the osteotomy.The cancellous nature of the osteotomy surfaces provides frictional resistance to shearing so long as compression across the osteotomy surface is maintained.(1,4)

Wroblewski and Shelley used these principles in using a ‘chevron’ osteotomy and a spring loaded wiring system, achieving 98.1% union in 431 procedures(4,5). Different wiring techniques and various implant devices have been devised to help stabilise the trochanter against antero-posterior shear motion.

In reviewing the results of the conventional; monofilament wiring techniques Clarke,Shea and Bierbaum

(1979),reported loss of trochanteric fixation varying from 2.7 to19.4% and wire breakage from 17.2 to32%.(6)

Dall and Miles introduced their cable grip system in 1983 and reported 1.5 % nonunion and 3.1 % cable breakage rate after clinical trials for over four years in 321 hips(1). They highlighted the fact that multifilament cable had superior mechanical properities to monofilament wire and does not kink. Also the cable grip provides strong compression across the osteotomy surfaces.(1)

However, Ritter et al (9) in 1991 showed a 37.5% nonunion rate and 32.5 % cable breakage. They attributed this to use of stainless steel cable and metal reaction on contact with the titanium prosthesis. Silverton et al(1996) reported 25% nonunion and fraying and fragmentation of the cables , as well as osteolysis(10). In a six year evaluation of 223 revision hips, McCarthy et al reported 9% non union and 10% breakage rate(8).However, when they achieved bone to bone apposition, the non-union rate was 4%. We obtained 1.2% nonunion and 3% cable breakage rate in our series of 98 primary total hip arthroplasties.(see Table 2)

The distance of migration of the trochanter and it’s significance has been a much debated issue. The critical distance of migration beyond which abductor function is impaired has been reported from 1.5cm(Boardman) to 2 cm (Amstutz and Maki). Nutton and Checketts using load cells measured abductor power in 167 patients and concluded 3 cm was the critical distance, also supported by Johnston. We have used the radiological grading (7)in which the critical distance is beyond 3cm for the higher grades(3&4). This classification differentiates between grade 3 and 4 on the basis of necessity of surgery for non-union.(see table1)

In our series, the radiological grading showed that 89 patients (90.8%) had perfect apposition and union (Grade 1)(seefig.1,2) and 2 of these patients had single broken cable, not affecting union(fig.3). Eight patients(8.1%) had slight positional loss(1-3 cm) with union(Grade2).There was one patient (1.2%) with non-union requiring re-operation(Grade 4)( see fig.4,5). Careful analysis of the radiographs in our series did not reveal any fraying or fragmentation of the cables or any evidence of cable debris or osteolysis.

In conclusion, the Dall-miles cable grip system for trochanteric osteotomy fixation in primary THR has given us consistently good results, with 1.2% non-union rate and 3% cable breakage rate. In order to make any lasting recommendations, we would need a longer follow-up and a larger cohort of patients. A randomised prospective trial is needed to compare the D.M cable system with other wiring techniques.

1.Dall D.M, Miles A.W: Re-attachment of the greater trochanter.The use of the Trochanter cable-grip system JBJS:65B,No.1pp55-59 1983

2. Eftekar NS: Principles of total hip arthroplasty,Chapter 37: Trochanteric osteotomy complications.St Louis 1978, Mosby-Year book

3.Frankel A.,Booth R.E, Balderston R.A, : Complications of trochanteric osteotomy.Clin.Orthopaedics 1993 No.288:209-213

4.Glassman A.H: Complications of trochanteric osteotomy: Orth.Clin.of North america Vol23:no.2 apr’1992:321-333

5.Harris W.H,Jensen N.F: A system for trochanteric osteotomy and re-attachment for T.H.R with a ninety-nine percent union rate .Clin.Orthopaedics 1986 No.208:174-181

6.Harris W.H, Bal B.S,Maurer B.T: Trochanteric union following revision total hip arthroplasty.The Journal of Arthroplasty Vol.13 No.1 1998:29-33

7.Menon P.C, Griffiths W.E.G,Hook W.E: Trochanteric osteotomy in total hip arthroplasty .The Journal of Arthroplasty Vol.13 No.1 1998:92-96

8.McCarthy J.C, Bono J.V, Turner R.H: The outcome of trochanteric re-attachment in revision THR with a cable grip system with mean 6-year follow-up. Presented in AAOS annual meeting1999

9.Ritter M.A, Eizember L.M, Keating E.M: Trochanteric fixation by cable grip in hip replacement.JBJS1991:73-B:580-1.

10. Silverton C.D, Jacobs JJ: Complications of a cable grip system.The Journal of Arthroplasty Vol.11 No.4 1996:400-404

Fig.3: one year post op X-ray showing union with slight migration and broken cable ( Grade2)

Fig.5: Same patient as 4 after open reduction and screw fixation of trochanter.