Continuous distal migration and internal rotation of the C-stem ...

 HIP

Continuous distal migration and internal rotation of the C-stem prosthesis without any adverse clinical effects T. von Schewelov, Å. Carlsson, L. Sanzén, J. Besjakov From Department of Orthopaedics and Clinical Sciences, Lund University, Skane University Hospital, SE-205 02 Malmö, Sweden

AN RSA STUDY OF 33 PRIMARY TOTAL HIP ARTHROPLASTIES FOLLOWED FOR UP TO TEN YEARS

In 2005, we demonstrated that the polished triple-tapered C-stem at two years had migrated distally and rotated internally. From that series, 33 patients have now been followed radiologically, clinically and by radiostereometric analysis (RSA) for up to ten years. The distal migration within the cement mantle had continued and reached a mean of 2 mm (0.5 to 4.0) at ten years. Internal rotation, also within the cement mantle, was a mean 3.8° (external 1.6° to internal 6.6°) The cement mantle did not show any sign of migration or loosening in relation to the femoral bone. There were no clinical or radiological signs indicating that the migration or rotation within the cement mantle had had any adverse effects for the patients. Cite this article: Bone Joint J 2014;96-B:604–8.

 T. von Schewelov, MD, PhD, Orthopaedic Surgeon  Å. Carlsson , MD, PhD, Orthopaedic Surgeon  L. Sanzén , MD, PhD, Orthopaedic Surgeon Skane University Hospital, Department of Orthopaedics, S-205 02 Malmö, Sweden.  J. Besjakov , MD, PhD, Consultant in Radiology Skane University Hospital, Department of Radiology, S-205 02 Malmö, Sweden. Correspondence should be sent to Dr Med T. von Schewelov; e-mail: Thord.von_Schewelov@ med.lu.se ©2014 The British Editorial Society of Bone & Joint Surgery doi:10.1302/0301-620X.96B5. 33580 $2.00 Bone Joint J 2014;96-B:604–8. Received 28 November 2013; Accepted after revision 4 February 2014

604

We previously reported the radiostereometric analysis (RSA) of migration of the C-stem (DePuy International, Leeds, United Kingdom) up to two years.1 The C-stem is a triple-tapered polished stem designed to sink within the cement mantle in a similar mode as the Exeter stem (Howmedica International Ltd, London, United Kingdom). In the former design, distal migration is thought to enhance proximal loading of the femur.2 At two years we found that distal migration was similar to the Exeter stem but the C-stem exhibited a greater internal rotation than the Exeter. The subsequent migration pattern for the C-stem and any consequences have not previously been described. We now present the clinical, radiological and migratory pattern of the C-stem up to ten years.

Patients and Methods The patients and methods have been fully described in our previous paper.1 In summary, in 2002 36 hips in 36 patients with osteoarthritis had a primary total hip replacement (THR) using the C-stem stem and a cemented polyethylene acetabular component (Fig. 1). In total, two patients were excluded because of inadequate post-operative RSA examinations. Another patient, for whom one hip was part of the initial series, was excluded because of early bilateral radiological changes and continuous pain that led to early bilateral re-oper-

ations. We had suspected septic loosening but multiple cultures taken at revision were negative. From the original series, two patients died at five and seven years respectively, and three died between the seven and ten year follow-up. Three patients refused further follow-up, one after five years and two after seven years. This left 33 patients available for evaluation at two and five years, 30 patients at seven years and 25 at ten years. The Regional Ethical Review Board in Lund approved the study. Examinations within one week post-operatively and at three months, one, two, five, seven and ten years included clinical assessment, radiological analysis and RSA. For the clinical evaluation we used Harris hip score3 (HHS) and the Charnley score.4 The radiological examination included an anteroposterior (AP) view of the hip and pelvis and a lateral view of the femur. The films were viewed simultaneously by two of the authors in consensus (TvS and JB). Change of position and progressive and non-progressive radiolucent lines were looked for in the femur according to Gruen5 and around the cup according to DeLee and Charnley.6 Approximately eight tantalum beads, 0.8 mm in diameter, were inserted in the proximal femur at the primary operation. The cement was also labelled with a 1 mm bead at THE BONE & JOINT JOURNAL

CONTINUOUS DISTAL MIGRATION AND INTERNAL ROTATION OF THE C-STEM PROSTHESIS WITHOUT ANY ADVERSE CLINICAL EFFECTS

Fig. 1 Digital image of the C stem with centraliser and 22 mm steel head.

X migration Y migration Z migration Y migration cement

Migration (mm)

2

1

0

605

The latter displacement was calculated as transversal, distal, sagittal and total displacement, i.e. the length of the resulting vector. The latter has been referred to previously as maximum total point movement (MTPM).8 Segment migrations and rotations were calculated between the cement relative to the bone as well as the stem relative to the bone. The radiographs were digitised on a measurement table (Hasselblad Engineering, Gothenburg, Sweden) using linear gauges and a video camera with 16 × magnification. This method was subsequently exchanged for a digital method during the latter part of the study. The images were scanned at 16 bits/300 DPI resolutions with an Umax Mirage II scanner (UMAX Techville Inc., Dallas, Texas) and measured with UmRSA Digital Measure (RSA Biomedical, Umeå, Sweden) and analysed by UmRSA in the same way as with the manual measurements. The UmRSA Digital Measure uses least squares fitting of non-linear marker models to estimate the marker centre position, a technique that has been shown to maintain or improve the precision compared with manual measurements.9,10 The detection limit for significant movements over time with 99% confidence intervals (CI), was calculated using double examinations. The detection limit was +/- 0.2 mm for the longitudinal and transverse axis and +/0.4 mm along the sagittal axis and for MTPM. The limit for significant rotation was 0.3 mm around the transverse and sagittal axis and 0.6 mm around the longitudinal axis. Statistical analysis. The Wilcoxon matched pair test was used for calculating prosthetic movements between measurements. Results with a p-value ≤ 0.05 were considered statistically significant.

-1

-2 3 6 12 24 (19)(19) (22) (19)

36 (16)

60 (20)

84 (19)

120 (14)

Post-operative time (mths) Fig. 2 Graph showing stem migration in relation to the bone along the longitudinal axis (Y), along transverse axis (X) and sagittal axis (Z). Cement movement along the longitudinal axis is shown in relation to the bone (Y migration cement). Number of radiostereometric analysis (RSA) examinations at each time point in brackets (includes only stems with markers mounted).

implantation. In 26 of the 33 patients (78%) a 0.8 mm bead was factory mounted by DePuy on a tower on the shoulder and the tip of the prostheses. Seven larger stems sizes 4 to 7 were unmarked and could thus only be analysed for migration. RSA was performed with the patient in the supine position using the uniplanar technique.7 Migration of the modular head was evaluated relative to the femoral bone. VOL. 96-B, No. 5, MAY 2014

Results Except for the patient with early bilateral loosening reported above, no post-operative complications were recorded. The Charnley score for pain was a mean of 3.0 (2 to 6) pre-operatively and at ten years a mean of 5.8 (4 to 6). Corresponding values pre-operatively and at ten years were for function a mean of 2.8 (2 to 5) and 5.3 (2 to 6), respectively and for range of movement (ROM) a mean of 4.1 (2 to 6), and 6.0 (5 to 6). The mean HHS for pain was 17 (10 to 30) pre-operatively and 42 (20 to 44) at ten years and. The mean total score was 47 (27 to 60) pre-operatively and 90 (58 to 95) at ten years. No patient experienced a dislocation post-operatively. Post-operative analysis of stem position and the quality of cementing has been presented in our previous report.1 In the present radiological analysis there were no signs of loosening observed of the femoral components. In one case a thin gap could be observed between the stem and the cement in the anterior superior part of the femur. There was no sign of loosening or wear around the acetabular components evidenced by the absence of any progressive radiolucent lines lines or change of component position.6 The migration patterns and the number of examinations possible to analyse are presented in Figures 2, 3 and 4.

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T. VON SCHEWELOV, Å. CARLSSON, L. SANZÉN, J. BESJAKOV

4 4 3 3

0 -1

Y rotation X rotation Z rotation Y rotation cement

-2 -3

Migration mm

1

Rotation (º)

MTPM X migration Y migration Z migration

2

2

1 0 -1 -2 -3

-4 3 6 12 24 (19)(19) (22) (19)

36 (16)

60 (20)

84 (19)

-4

120 (14)

3 6 12 24 36 (19)(19) (22) (19) (16)

Post-operative time (mths)

60 (20)

84 (19)

120 (14)

Post-operative time (mths)

Fig. 3

Fig. 4

Graph showing the stem rotation in relation to the bone around the longitudinal axis (Y), transverse axis (X) and sagittal axis (Z). The rotation of the cement mantle is shown in relation to the bone around the longitudinal axis (Y rotation cement). Number of radiostereometric analysis (RSA) examinations in brackets (only stems with markers mounted).

Graph showing the mean total point migration of the head of the stem in relation to the bone along the longitudinal axis (Y), transverse axis (X), sagittal axis (Z) and mean total point movement (MTPM). Number of RSA examinations at each time point n brackets (includes all stems).

Table I. Distal migration and internal rotation of different polished stem designs Reference

Stem/cement*

Alfaro-Adrian13† Stefansdottir14 McCalden15

Exeter / CMW Exeter / Palacos CPCS / Exeter Simplex

Nieuwenhuijse12 Murray11‡ Present

Exeter / Simplex Exeter / not reported C-stem / Palacos

Distal migration (mm), years

Internal rotation (degrees), years

2

2

1.2 1.34 CPCS 0.77 / Exeter 1.25 1.42 0.92 1.36

5

10

1.77

1.89 1.71

5

10

1.2 1.6 CPCS 1.61° / Exeter 0.59° 2.13 1.28 2.06

1.42 0.71 1.6

1.7 2.66

1.82 1.22 3.78

* CMW, (DePuy International, Leeds United Kingdom); CPCS (Smith & Nephew, Memphis, Tennessee); Palacos (Zimmer, Warsaw, Indiana); Simplex (Stryker, Mahwah, New Jersey) † RSA technique based on a geometric model of the stem and not on markers fixed to it ‡ RSA technique based on a geometric model of the tip or head of the stem and not on markers fixed to it. Distal migration of the tip of the stem and internal rotation of the head

There was a continuous distal migration of the stems during the whole observation period (Fig. 2). There were also a continuous rotation (Fig. 3) of the stems around the longitudinal (y) axis in the dorsal direction (internal rotation) (p values were between < 0.001 and 0.014) except between 12 and 24 months (p = 0.06). However, there was no corresponding distal migration or rotation of the cement in relation to the bone (Figs. 2 and 3). The maximal distal migration was 4 mm, with nine of 26 stems migrating distally between 2 mm and 4 mm. Max-

imal internal rotation was 6.6°, with nine stems rotating more than 4°. MTPM of the femoral head in relation to the bone (Fig. 4) was 5.8 mm. MTPM was more than 2 mm in 28 of the 33 patients and more than 4 mm in seven hips.

Discussion We found that the C-stems continued to migrate distally and to rotate internally within the cement mantle up to ten years post-surgery. In one case a radiological lucency or ‘gap’ could be observed between the cement mantle and at THE BONE & JOINT JOURNAL

CONTINUOUS DISTAL MIGRATION AND INTERNAL ROTATION OF THE C-STEM PROSTHESIS WITHOUT ANY ADVERSE CLINICAL EFFECTS

the shoulder of the stem. There were no signs of loosening of the cement mantle from the femoral bone in any case, even though the distal migration was up to 4 mm, MTPM 5.8 mm and internal rotation 6.6°. Clinical and radiological results were good overall and at least as good as in other comparable studies.11,12 There were no revisions other than the bilateral case described above, and no dislocations. Distal migration was comparable with the Exeter stem whereas the C-stem internally rotates more than the Exeter stem (Table I).11-15 The performance of the C-stem in general use was satisfactory according to the Ninth Annual Report from the National Joint Registry for England and Wales.16 With a revision rate of only 1.37% (95% CI 0.94 to 1.99) at seven years for the C-stem combined with the Elite Plus Ogee acetabular component it is comparable with the 1.47% (95% CI 1.19 to 1.81) revision rate for the Exeter prosthesis combined with the same acetabular implant. The C-stem revision rate is also comparable with the 2.52% (95% CI 1.96 to 3.23) for the CPT stem with the ZCA acetabular component (both Zimmer, Warsaw, Indiana). In the Australian Registry 2012,17 the Cumulated Risk of Revision at ten years is 7.8% (95% CI 3.4 to 17.1) for C-stem / Elite Plus (DePuy International, Leeds, United Kingdom) combination. The corresponding results for the Exeter stem combined with an Exeter acetabular component is 3.9% (95% CI 2.8 to 5.4), for the MS 30 stem combined with a low profile acetabular component (both Zimmer, Winterthur, Switzerland) 2.2% (95% CI 1.1 to 4.6) and for the CPT stem combined with a ZCA implant 5.1% (95% CI 2.9 to 9.1). The rather large distal migration and internal rotation in some patients might cause concern for dislocation. However, in 2012 Purbach et al18 reported that only two out of 621 C-stems implanted during a 15-year period had been revised because of dislocation. We accept that the stem migrating within the cement mantle could generate cement particles thereby inducing accelerated polyethylene wear. Unfortunately we did not mark our acetabular components with tantalum beads and are therefore unable to measure wear. However, the revision rates from the national joint registers in England and Wales, and Australia include acetabular component revision but remain comparable with those for other wellperforming cemented THRs. The original C-stem have since been replaced by the C-stem AMT, which has a 12/14 mini-taper in order to optimise use with advanced bearings and to increase ROM. In addition, the AMT version for the C-stem also offers an increased range of offsets but the intramedullary geometry is unchanged. However, the lateral shoulder has been raised, with the aim to achieve a clear neck resection level and improve visibility during stem insertion. Whether this improves the migratory pattern of the C-stem AMT has not been investigated. When we planned this study we aimed at describing the micro-movement pattern of the C-stem with clinical and VOL. 96-B, No. 5, MAY 2014

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radiological results only up to two years. As we found a progressive internal rotation which exceeded that reported for the well-performing Exeter stem we continued the follow-up. However, patients were lost to follow-up due to unrelated ill-health and death, so that there were only 25 of 33 patients remaining at ten years. Over time some of the tantalum beads within the bone became unstable and made it impossible to use several of the examinations for RSA studies. Because of this only 14 stems remained for RSA assessment of rotation and migration at ten years. However, as the method is so precise we believe that our results remain valid. The C-stem continues to migrate distally and internally rotate within the well-fixed cement mantle up to ten years, but within our series has so far not resulted in any adverse events or increased revision frequency. No benefits in any form have been received or will be received from a commercial party related directly or indirectly to the subject of this article. We would like to acknowledge the services of G. Nilsson who kept track of all patients and P. Markusson for making the RSA measurements. This article was primary edited by G. Scott and first proof edited by D. Rowley.

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15. McCalden RW, Charron KD, Yuan X, et al. Randomised controlled trial comparing early migration of two collarless polished cemented stems using radiostereometric analysis. J Bone Joint Surg [Br] 2010;92-B:935–940.

17. No authors listed. Australian Orthopaedic Association: National Joint Replacement Registry: Annual Report, 2012 http://www.aoa.org.au/ (date last accessed 5 February 2014).

16. No authors listed. National Joint Registry for England and Wales: 9th Annual Report, 2012. http://www.njrcentre.org.uk/njrcentre/default.aspx. (date last accessed 5 February 2014).

18. Purbach B, Kay PR, Siney PD, Fleming PA, Wroblewski BM. The C-stem in clinical practice: fifteen-year follow-up of a triple tapered polished cemented stem. J Arthroplasty 2013;28:1367–1371.

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