North Hampshire Hospital Trust, Aldermaston Road, Basingstoke, Hampshire. RG24 9NA, UK. Correspondence should be sent to Dr G. W. Blunn. ©2000 British ...
A comparison of bone remodelling around hydroxyapatite-coated, porous-coated and grit-blasted hip replacements retrieved at post-mortem M. J. Coathup, G. W. Blunn, N. Flynn, C. Williams, N. P. Thomas From the Royal National Orthopaedic Hospital, Stanmore and Basingstoke General Hospital, England
e investigated the implant-bone interface around one design of femoral stem, proximally coated with either a plasma-sprayed porous coating (plain porous) or a hydroxyapatite porous coating (porous HA), or which had been grit-blasted (Interlok). Of 165 patients implanted with a Bimetric hip hemiarthroplasty (Biomet, Bridgend, UK) specimens were retrieved from 58 at post-mortem. We estimated ingrowth and attachment of bone to the surface of the implant in 21 of these, eight plain porous, seven porous HA and six Interlok, using image analysis and light morphometric techniques. The amount of HA coating was also quantified. There was significantly more ingrowth (p = 0.012) and attachment of bone (p < 0.05) to the porous HA surface (mean bone ingrowth 29.093 ± 2.019%; mean bone attachment 37.287 ± 2.489%) than to the plain porous surface (mean bone ingrowth 21.762 ± 2.068%; mean bone attachment 18.9411 ± 1.971%). There was no significant difference in attachment between the plain porous and Interlok surfaces. Bone grew more evenly over the surface of the HA coating whereas on the porous surface, bone ingrowth and attachment occurred more on the distal and medial parts of the coated surface. No significant differences in the volume of HA were found with the passage of time. This study shows that HA coating increases the amount of ingrowth and attachment of bone and leads to a more even distribution of bone over the surface of the implant. This may have implications in reducing stress shielding and limiting osteolysis induced by wear particles.
The use of hydroxyapatite (HA) coating has been advocated in order to increase the attachment of bone to metal implants. Many animal as well as clinical studies have demonstrated the osseoconductive properties of HA and the 1,2 results at six to eight years are excellent. Bone apposition 3 appears to be well advanced as early as three weeks, and some studies have shown it to be greater than 90% at 96 4 weeks. Although there is concern that HA resorbs with time and that the release of HA debris may have adverse 5 effects, the clinical results reported so far for HA-coated components suggest that at present this is not a significant problem. Several reports of the outcome after the insertion of porous-coated uncemented implants have shown good 6-8 results. Most studies found some degree of bone 9-12 with the mean extent reported to ingrowth into the pores 9,12 13 be in the range of 5% to 39.2% of the available pore volume. An HA coating has been advocated in order to reduce the effects of debonding and to encourage bone ingrowth and attachment to a porous surface. Several studies have examined the use of an HA surface coating on porous-coated implants. Some have reported that there is no clinical 14 advantage while others have demonstrated a significant 15,16 increase in bone ingrowth. We have investigated bone ingrowth and attachment to an HA-coated porous titanium surface, a plain porous titanium surface and a roughened titanium (Interlok) surface finish in one femoral design from specimens obtained at post-mortem.
J Bone Joint Surg [Br] 2000;82-B:118-123. Received 24 March 1999; Accepted after revision 21 September 1999
We treated 165 patients with a mean age of 84.8 years (79 to 92) for fracture of the neck of the femur using a Bimetric hip hemiarthroplasty (Biomet, Bridgend, UK) at the Basingstoke General Hospital, Hampshire. Each patient randomly received a femoral component with either a plain porous, a porous HA or an Interlok surface on the proximal region of the femoral stem. The porous titanium surfaces were applied to the surface of the implant using a plasma spray process. The HA coatings were applied by the same process and had a mean crystallinity value of >85% and a mean thickness of 50 m. The Interlok surface was gritblasted titanium with an Ra value of 6 m. Before surgery,
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M. J. Coathup, BSc, PhD, Research Fellow G. W. Blunn, PhD, Professor and Head of Department Centre for Biomedical Engineering, University College of London, Royal National Orthopaedic Hospital, Brockley Hill, Stanmore, Middlesex HA7 4LP, UK. N. Flynn, FRCS, Consultant Orthopaedic Surgeon C. Williams, FRCS, Consultant Orthopaedic Surgeon N. P. Thomas, FRCS, Consultant Orthopaedic Surgeon North Hampshire Hospital Trust, Aldermaston Road, Basingstoke, Hampshire RG24 9NA, UK. Correspondence should be sent to Dr G. W. Blunn. ©2000 British Editorial Society of Bone and Joint Surgery 0301-620X/00/110062 $2.00 118
Materials and Methods
THE JOURNAL OF BONE AND JOINT SURGERY
A COMPARISON OF BONE REMODELLING AROUND HIP REPLACEMENTS RETRIEVED AT POST-MORTEM
permission was sought from the patients and their next of kin to retrieve the implants at the time of death. These and the associated femora were collected at postmortem. Overall, 58 specimens were retrieved: 15 Interlok (mean duration 2.5 years; range 4 to 938 days), 24 porous-coated (mean duration 4.5 years; range 2 to 1572 days) and 19 HA-coated (mean duration 2.8 years; range 2 to 1057 days). Because of the high number of implants retrieved and taking into consideration the cost, the lengthy processing of the specimens and the preparation necessary to produce histological thin sections, eight plain porouscoated specimens, seven porous HA-coated specimens and six Interlok specimens were analysed. The duration of the implants was as far as possible matched by selection into one of three groups according to their length of time in vivo: 0 to 1 year (3 porous HA, 173, 261 and 345 days; 2 plain porous, 109 and 243 days; 3 Interlok, 38, 72 and 123 days); 1 to 2 years (2 porous HA, 442 and 660 days; 3 plain porous, 452, 573 and 650 days; 1 Interlok, 607 days); and 2 years and over (2 porous HA, 941 and 1057 days; 3 plain porous, 908, 1094 and 1572 days; 2 Interlok, 864 and 928 days). On retrieval, the specimens were fixed in 10% formaldehyde solution and excess soft tissue was removed. The proximal region of each femoral component (i.e., the coated area being investigated) was cut using an Exotom cut-off machine (Struers), into a proximal region (F1), a mid region (F2) and a distal region (F3) (Fig. 1). These specimens were then prepared for hard-tissue processing. Thin sections (
