TaperFit. Cemented Femoral Stem Product rationale

Transcription

1 TaperFit Cemented Femoral Stem Product rationale

2 TaperFit Design History Function TaperFit cemented femoral stems have been in use for over 17 years and are clinically proven to produce excellent results 1,2,3,4. Manufactured from a high strength, high nitrogen stainless steel alloy*, the comprehensive range of 36, 38, 45 and 50mm offset stems allows the surgeon to fine tune leg length, offset and femoral fill intra-operatively and independently of each other. TaperFit is suitable for use with a wide range of surgical philosophies and approaches. The trunnion is compatible with Corin s comprehensive range of cobalt chrome alloy* heads and BIOLOX delta ceramic heads for total hip replacement, as well as bipolar and unipolar heads for hemiarthroplasty/fracture management. Compatible acetabular implant options include: Trinity cementless advanced bearing acetabular system incorporating: Ultra high molecular weight polyethylene (UHMWPE) Highly cross-linked UHMWPE ECiMa (vitamin E stabilised) highly cross-linked UHMWPE BIOLOX delta ceramic liners Cenator cemented UHMWPE cup. Cormet cementless metal-on-metal resurfacing cup. 2 *BS EN ISO 21534

3 100% survivorship for aseptic loosening at 10 years 3 3

4 TaperFit Design A winged polymethylmethacrylate (PMMA) centraliser-void is pushed onto the distal tip of the stem: Manufactured from the same material as bone cement, this device repolymerises and becomes one with the cement mantle as it cures. The wings on the device push against the endosteum to help centralise the distal tip for better alignment during introduction within the uncured bone cement. The void prevents the tip of the stem from being end-bearing, thus allowing the stem to act freely as a true taper. The stem s square lateral shoulder is designed to enhance both visualisation of proximal implant position and increase pressurisation within the greater trochanter via proximal fill during introduction into uncured bone cement. This feature may also improve rotational stability in the longer term. 4

5 One of the most important factors in successful total hip replacement is ensuring the central placement of the stem within the bone cement. Malalignment of the prosthesis has been shown to correlate directly with early loosening and failure 5. The lateral shoulder of the TaperFit stem has a recess for the dedicated in-line introducer. This instrument fits to the stem securely, providing: Excellent axial and rotational control during insertion. Intuitive in-line/axial stem introduction. Intra-operative choice of/transition between captive and semicaptive stem introduction which reduces the likelihood of cement void creation. The elliptical/split distal end of the stem introducer fits into the elliptical hole on the lateral shoulder of the definitive implant. To load the stem, pull the trigger on the introducer to ensure the locking mechanism is loose (Fig 1). In order to lock the stem onto the introducer, push the rectangular button near to the handle until it clicks (Fig 2). To release the stem, pull the trigger slowly to re-close the elliptical/ split distal tip of the introducer (Fig 3). (Fig 1) Load stem (Fig 2) Lock stem (Fig 3) Release stem 5

6 TaperFit Body weight The TaperFit stem is polished so it always decouples from, but firmly wedges within, the cured cement mantle. The downward forces exerted by body weight are safely converted into essentially horizontal compressive forces 6 that play to the strengths of bone cement. These quasi-physiological radial forces are, in turn, transferred to the femur in such a way that stress shielding is limited and bone stock is preserved in accordance with Wolff s law of bone adaptation. The collarless, polished and tapered design exploits the cement creep phenomenon of cumulative deformation not insignificant when at body temperature and in the presence of intramedullary fat 7,8. Micro-movement in any prosthesis-bone system is inevitable. However because TaperFit has no surface or structural features preventing it from acting as a self-tightening wedge, micro-movement takes place preferentially at the stem-cement interface. Movement at the cement-bone interface, which must be seen as true loosening, is therefore limited 6. This design of femoral stem becomes progressively more secure as it subsides, in a controlled and self-limiting manner, without causing abrasion within the cement mantle until stable equilibrium is achieved 6. 6

7 Polished stem Cement mantle Bone The highly-polished* surface of the TaperFit stem greatly reduces the risk of micromotioninduced abrasion at the stem-cement interface. Implant stability is secured through the double taper, which permits self-tightening via controlled distal migration. This occurs essentially at the same rate as seen with the first commercially available stem of this design type 4. Matt stem Cement mantle Bone Conversely, the fine but rough surface features on a matt stem interlock with the cured cement mantle. This prevents the conversion of the harmful vertical shear forces into the advantageous radial compressive forces. The cement-bone interface therefore has to deal with these adverse loosening forces. The matt stem-cement interface is also subjected to abrasive wear which is also linked to loosening 6. The TaperFit stem design allows for subsidence without damaging the cement-bone interface 6 *Ra = 0.073µm 7

8 TaperFit The TaperFit stem has over 17 years of successful clinical history supporting its use. Since TaperFit was first introduced in 1995, it has remained unchanged with only minor enhancements to the extramedullary introducer holes. These holes, situated above the average resection line, were modified for improved fatigue performance* and ease of implantation. Launched 1995 Modified 2007* Modified x angulated drill holes 2x rounded drill holes 1x rounded elliptical dove-tail hole 8 *CDH stem and 38mm offset size 1 stem only

9 -5mm +/-0mm +5mm Each implant has a dedicated over-sized rasp which produces an optimum 2mm cement mantle. A trial reduction can be performed with the rasp in situ so that offset and implant depth/leg length may be accurately assessed using a pin through one of the three medial holes on the rasp at the level of the resected femoral neck. The position of these holes corresponds to the marking on the stem so that the trialled position can be accurately replicated with the definitive femoral component. Assuming that the rasp is impacted to the centre hole in the first instance then the pin is inserted through the more distal (+5mm) hole if an increased leg length is required. If a leg length reduction is required then the rasp is simply impacted further taking care not to fracture the proximal femur. 9

10 TaperFit History Why collarless? During the late 1960s, one of the most common problems associated with THR with cemented collared femoral implants was calcar resorption. This complication was routinely observed at follow-up X-ray. The medial collars historically used were intended to load the proximal femur. However, even when great care was taken to obtain intimate bony contact between the underside of the collar and the resected surface of the calcar during surgery, proximal femoral resorption remained a concern. Collars were also seen to provide a pivot point about which excessive distal stem movement often occurred. For these reasons, collarless stem designs were proposed. Why polished? The rationale for the early, straight, collarless, tapered designs to be made from polished stainless steel alloy arose from a historical precedent. In the late 1960s, the accepted industry standard finish for EN58J stainless steel alloy implants was polishing. This historical default position has, however, been validated by clinical results over time 1,2,3,4,6,9. Why tapered? Around the same time, another common observation after THR with cemented femoral implants was component malpositioning. This was seen on immediate post-operative X-rays and often led to revisions 5. This was seen more frequently with curved devices as the tip of the stem is more difficult to guide into position than the tip of a straight stem. For this reason a straight tapered stem design was proposed. Originally straight double tapers were proposed simply because they would provide for more efficient extrusion of doughy bone cement. However, over the last 40 years, a more detailed understanding of the forces endured and transmitted by hip prostheses has been developed. 10

11 Collarless, polished, tapered functionally inseparable features 11

12 TaperFit Function TaperFit stems have produced excellent clinical results since launch in ,2,3,4. The TaperFit total hip system. Interim results in an unselected consecutive cohort 2 No revisions for obvious clinical stem loosening. Kaplan-Meier Survivorship: 97.7% at 7 years. The TaperFit total hip system 10 year results. An unselected consecutive cohort 3 Kaplan-Meier Survivorship: 100.0% at 10 years for aseptic lossening. 12

13 Stem subsidence as a function of taper angle 1 Radiographic assessment of subsidence in: 320 size 1 stems 347 size 2 stems 117 size 3 stems 33 size 4 stems No statistically significant difference in distal migration between four sizes even though the stem geometry varies considerably across the range. Subsidence rates were similar to those observed by the developers of the Exeter stem. There were no failures due to aseptic stem loosening. Distal migration of the femoral stem within the cement mantle. A comparison between the TaperFit and the Exeter prostheses 4. Subsidence at 2 years postoperatively: 1.32mm for the TaperFit stem 1.30mm for the Exeter stem 13

14 TaperFit Fractured neck of femur In September 2007 the British Orthopaedic Association published a report in collaboration with the British Geriatric Society, on the care of patients with fragility fracture. The report stated that the use of cemented arthroplasty is associated with a lower aseptic loosening rate, may also make the hip less painful and improves function. Accordingly, it should usually be preferred to a cementless technique 10. In 2011, a report produced in the UK by the National Clinical Guideline Centre (NCGC) and the National Institute for Health and Clinical Excellence (NICE) recommended the use of a proven femoral stem design rather than Austin Moore or Thompson stems 11 for treating fractured necks of femur. A systematic review 12 of randomised controlled trials compared the outcomes of cemented and uncemented hemiarthroplasty for treatment of intracapsular hip fractures. Eight studies involving 1169 patients were determined to be appropriate for the required meta-analysis. The report found a lower reduction in mobility score for those treated with a cemented prosthesis and fewer patients with residual pain in the hip and lower pain score (signifying less pain) for those treated with a cemented prosthesis. Additionally the authors concluded that there is good evidence that the use of cement during hemiarthroplasty will reduce the amount of residual hip pain and also allow better restoration of function plus that there is no evidence of significant adverse effects of cement on mortality or other complications. The TaperFit stem when used with Corin s range of hemiarthroplasty unipolar and bipolar heads * represents an excellent choice for treating fractured necks of femur. The pre-assembled captive head provides maximum security and ease of use. The eccentric, selfcentring bipolar design ensures against the adverse effects of varus positioning. 14 *Available with short, standard and long necks to help optimise joint biomechanics.

15 Cemented femoral stem providing excellent clinical results 1,2,3,4 15

16 TaperFit Stem sizes Offset Size* Offset Neck length Stem length CDH mm offset size mm offset size mm offset size mm offset size mm offset size mm offset size mm offset size mm offset size mm offset size mm offset size mm offset size mm offset size mm offset size mm offset size mm offset size Neck length Stem length 16 *Standardised CCD angle of 125º

17 Based on biomechanical principles clinically proven over more than 40 years 9 17

18 TaperFit Cement restrictor sizes Corin has developed a range of intra-medullary (IM) sizers and cement restrictors which are compatible for use with the TaperFit stem and modern cement pressurisation techniques. Major diameter Restrictor size (mm) Minor diameter (mm) Major diameter (mm) Core diameter (mm) IM size recommendations mm Ø < 12mm mm Ø < 16mm mm Ø < 20mm mm Ø < 24mm Core diameter 18 Minor diameter

19 Hip continuum of care 19

20 References: : 1. Hussein S, Finlayson D. Stem subsidence as a function of taper angle. J Bone Joint Surg [Br]. Vol 90-B, Issue SUPP III, Finlayson D, Baird K, Barnett K, Nelson R. The TaperFit total hip interim results an unselected consecutive cohort. Data on file at Corin, Finlayson D, Baird K, Barnett K, Nelson R. The TaperFit total hip system 10 year results an unselected consecutive cohort. Data on file at Corin, McGill D, Spencer S, Finlayson D. Distal Migration of the TaperFit femoral stem within the cement mantle: a comparison with the Exeter prosthesis. Data on file at Corin, Ramos JL, Pandit HG, Edwards S, Grover ML. Lateral approach to the hip; does it predispose to malalignment of the femoral component in total hip arthroplasty? British Orthopaedic Association, Annual Congress 1999, Glasgow, Free Paper Session Timperley AJ, Gie GA, Lee AJC, et al. The femoral component as a taper in cemented total hip arthroplasty. J Bone Joint Surg 1993;75-B (Suppl I): Lee AJC, Perkins RD, Ling RSM. Time-dependant properties of polymethylmethacrylate bone cement. In: (Ed) Older MJO: Implant Bone Interface. Springer-Verlag. London, Berlin, Heidelberg, New York, Paris, Tokyo, Hong Kong. 1990: Simon JP. The effect of body temperature and the uptake of intramedullary fat on the mechanical and time dependant properties of polymethylmethacrylate. Experimental work. In: Restoration of bone stock with impacted cancellous allografts and cement in revision of the femoral component in total hip arthroplasty. A clinical and biomechanical study. Thesis Catholic University of Leuven 1994: Ling RSM, Charity J, Lee AJC, Whitehouse SL, Timperley AJ, Gie GA. The long-term results of the original Exeter polished cemented femoral component a follow-up report. J Arthroplasty. Vol. 24 No The care of patients with fragility fracture. A report published by the British Orthopaedic Association in collaboration with the British Geriatric Society, September The management of hip fracture in adults methods, evidence and guidance. Published by the National Clinical Guideline Centre (NCGC) at The Royal College of Physicians and the National Institute for Health and Clinical Excellence (NICE), England Azegami S, Gurusamy KS, Parker MJ. Cemented versus uncemented hemiarthroplasty for hip fractures: a systematic review of randomised controlled trials. Hip Int (2011;05) The Corinium Centre Cirencester, GL7 1YJ t: +44 (0) f: +44 (0) e: info@coringroup.com Printed on 9lives 80 which contains 80% total recycled fibre and is produced at a mill which holds the ISO for Environmental Management Systems. The pulp is bleached using Elemental Chlorine Free processes. BIOLOX delta is a registered trademark of CeramTec 2011 Corin P No I1154 Rev ECR 11223