G Holt, A Arthur, D Frame*, A Muirhead
Department of Orthopaedic and Trauma Surgery, The Ayr Hospital, Dalmellington Road, Ayr
*West of Scotland Blood Transfusion Service, Gartnavel General Hospital, Great Western Road, Glasgow
Correspondence to: Mr Graeme Holt, Flat 4/2, 112 Lancefield Quay, Glasgow. United Kingdom. G3 8HR.
E-mail: graemeholt@btinternet.com
SMJ 2004 49(4): 146-148
Aim: To assess the efficiency of skeletal allograft collection from patients undergoing primary joint arthroplasty at a District General Orthopaedic Unit. Methods: A two cycle audit was performed. Between cycles procedural changes were implemented to improve the efficiency of allograft collection. The discard rate of donated allograft was also assessed during each cycle. Results: Initially 80 patients were identified. Eight (8/ 80) did not donate allograft due to medical contraindications. Two (2/80) patients underwent intra-operative autologous born grafting. Allograft was not collected from 22 (22/70) suitable patients. As such only 68.6% of suitable bone was collected by the West of Scotland Blood Transfusion Service (WSBTS). Subsequently 100 patients were studied. Twenty-eight (28/100) patients did not donate allograft due to medical contra-indications. Two (2/100) patients underwent intra-operative autologous bone grafting. Eight (8/70) allografts were discarded as a result of logistical problems. As such 88.9% of suitable allograft was collected. Initially 29% of all allograft donated was rejected due to poor patient selection. This subsequently fell to 9.4%. Conclusion: By auditing the collection process a significant improvement(c2=7.17 df=1 p=0.001) in the efficiency of allograft collection was achieved. This was complemented by a significant reduction(c2=6.09 df=1 p=0.05) in the proportion of unsuitable allograft donated to the WSBTS.
Revision arthroplasty surgery is frequently complicated by the need to restore reduced native bone stock as a consequence of osteolysis. There are a variety of materials available to the surgeon to manage this problem, each with its inherent advantages and disadvantages. Autologous bone transplant is frequently employed when the quantity of bone required at the recipient site is relatively small. However there is significant morbidity associated with harvesting autologous bone and the quantity of graft available is limited.1
In circumstances where there is a more significant decrease in native bone stock, skeletal allograft may be used to restore the deficiency. To prevent a host-versus-graft immuneresponse, allogenic bone is processed by deep-freezing to eliminate the cellular component of the graft. This permits tissue transplant without prior HLA tissue-typing and reduces the risk of transplant associated infection.2 However, as a consequence of processing, allogenic bone does not provide the osteogenic properties of viable autograft.3
In Scotland, the Scottish National Blood Transfusion Service (SNBTS) is the principal collection agent and provider of allogenic bone. It has five collection centres based in Glasgow, Edinburgh, Dundee, Aberdeen and Inverness. Cancellous allograft is currently harvested from patients undergoing elective primary total hip and knee arthroplasty surgery following exclusion of unsuitable patients by stringent selection criteria. (Table 1.)
Table1. (Source – Scottish National Blood Transfusion Centre)
Contraindications to Skeletal Allograft Harvest |
|
Age less than 18 years. |
|
History of drug abuse. |
|
Chronic or high dose steroid administration. |
|
History of vCJD
infection. |
|
Previous history of malignancy. |
|
Inflammatory arthritis. |
|
Dementia or chronic neurological disease. |
|
Recent immunisation with a live vaccine. |
|
Positive Hepatitis B or C serology. |
|
Positive HIV serology or positive risk factors for HIV infection. |
|
Positive VDRL serology. |
|
History of treatment with growth hormone. |
Donors are screened for serological markers including HIV, Hepatitis B, Hepatitis C, and VDRL. In addition culture swabs are taken at the time of graft harvest in order to identify bacterial or fungal contamination. If these investigations are negative the bone is deep-frozen to -70oC and quarantined for six months. The donor is subsequently re-tested prior to the allograft being released for use. Approximately 18% of harvested femoral heads are found to be contaminated with bacteria or fungi.5
Allogeneic bone is the second most commonly transplanted human tissue after blood.4 It may be used to promote osteogenesis between adjacent bones or to fill cavities created by excision of bone cysts or tumour deposits. However the most common indication for the use of skeletal allograft is in revision hip arthroplasty surgery.2 In this circumstance morcellised allograft is used to replace bone deficiency following implant failure. The demand for allogenic bone continues to rise for several reasons. Favourable outcomes have been published in a number of series reporting its use in revision hip arthroplasty.6,7 In addition, the number of revision procedures for total hip arthroplasty rose in Scotland from 612 in 1993 to 1319 by the year 2000.8 The technique of impaction grafting has further contributed to increased demand as up to five femoral heads may be used in a single procedure. It was previously estimated that current source of allogenic bone would be sufficient to meet demand.9 However, up to half of all patients undergoing joint replacement surgery are unsuitable donors.10
It should also be noted that not all bone donated to the SNBTS is suitable for issue. A significant number of donations are discarded after collection due to stringent guidelines laid down by the SNBTS.11 Consequently there has been concern in recent years regarding the supply and demand of allogenic bone graft in the United Kingdom.8 Graph 1 illustrates data obtained from the West of Scotland Blood Transfusion Service (WSBTS) relating to bone allograft collection, discard and distribution between January 2000 and March 2003. This data confirms that the demand for skeletal allograft now exceeds supply from current sources. It is therefore imperative that orthopaedic units maximise the yield of allograft donation in order to attempt to address this shortfall.
To determine the efficiency of skeletal allograft collection from patients undergoing elective primary knee and hip arthroplasty surgery. It was agreed that all suitable patients should be requested to give consent for bone allograft harvest. However it was accepted that up to 40%1 of patients would be unsuitable for recruitment as a consequence of medical contraindications.
A two-cycle audit was performed, the first of which was conducted on a retrospective basis. Data was collected from hospital case-notes, theatre records and WSBTS records regarding whether bone donation took place. If it did not the reason for this was identified. After the results of the first audit cycle were available, changes were implemented to improve the efficiency of allograft collection. The second cycle was subsequently performed on a prospective basis. Each suitable patient was identified by the orthopaedic theatre team and a data set completed. If bone donation did not occur then the reason for this was recorded.
Six months after the final donation had taken place data was collected from the WSBTS regarding the discard rate of collected allografts.
During the first audit cycle a total of 80 patients were identified. Eight (10%) patients did not donate bone as a result of medical contraindications. Two (2.5%) patients underwent intraoperative autologous grafting. One (1.25%) sample was discarded as a result of contamination during harvest and a further sample was discarded as no transport was available for collection. Of the remaining 68 patients, 20 (25%) did not donate allograft, despite having no identified medical contraindications to do so. Of this group, 5 (18.75%) patients had given consent for donation, whilst there was no record of consent in the other 5 (6.25%) individuals. Therefore only 68.6% of suitable allograft was collected by the WSBTS.
Subsequently, theatre staff involved in the allograft collection process were interviewed in order to identify other reasons for shortfalls in donation. These included inadequate refrigerated storage facilities and a lack of sterile storage containers for harvested allografts. Any allograft not stored in the correct manner is automatically deemed unsuitable for collection by the WSBTS. In addition there was a general lack of awareness among medical staff concerning patient selection and recruitment. Similarly there was no formal unit policy regarding who was responsible for obtaining patient consent adhering to the guidelines laid down by the SNBTS. These issues were addressed prior to commencing the second audit cycle.
During the second audit cycle 100 consecutive patients were identified. A total of 28 (28%) individuals were identified as having medical contraindications which prevented allograft donation. A further 2 patients underwent autologous bone grafting at the time of surgery. Of the remaining 72 grafts harvested, 8 were not collected as no transport to the bone bank was available. This represented 11.1% of suitable samples. The remaining 64 patients all donated bone. Therefore in the second cycle 88.9% of suitable allograft was collected. No patient declined to donate bone in either group. The Chi-squared test was applied which confirmed statistical significance c2=7.17 df=1 p=0.001.
Another aspect of the collection process subject to scrutiny was the proportion of samples donated to the WSBTS which were deemed unsuitable for future issue. During the first arm of the study 14 (29%) of the 48 grafts collected were discarded as a result of inadequate patient follow-up or medical contraindications not identified at the time of consent. During the second arm of the study a dedicated member of medical staff was allocated for the recruitment of patients. Of the samples donated during this period only six (9.4%) of the 64 grafts collected were deemed unsuitable for issue. This reduction was also statistically significant c2=6.09 df=1 p=0.05.
It is clear from the data presented in Graph 1. that current demand for human bone allograft cannot be met from present sources. There are a number of potential strategies available to potentially address this shortfall. Cancellous allograft may be harvested from human cadavers. This is the source for structural bone grafts, however in the United Kingdom it is not currently used for obtaining cancellous allograft. This source is unpredictable and places extra demands on medical staff and the patient’s next of kin. Adequate asepsis is often not achievable at the time of graft harvest, and bacterial contamination rates are higher than for live donors.4 In addition screening histories must be obtained from relatives. These may be incomplete, and the risk of transmissible infection remains unknown.12
An alternative option is to substitute or supplement allograft with synthetic bone substitute. A variety of synthetic materials are now available for use in orthopaedic surgery. These substitutes vary greatly in osteoconductivity, osteoinductivity, mechanical strength, and cost. Synthetic graft has the advantage that the risk of transmissible infection from donor to recipient is eliminated, a complication which has been reported in up to 10% of patients undergoing significant allograft transplant.2 However synthetic bone substitute tends to be expensive and relatively large quantities are required for filling the significant bone defects encountered in revision arthroplasty surgery.13 There is also a lack of clinical evidence regarding its long-term outcome in revision arthroplasty surgery.
A third strategy would be to maximise the efficiency of skeletal allograft donation from current sources. From the results of this study it is apparent that a statistically significant improvement in the yield of skeletal allograft can be achieved by effective audit of the collection process. This increase in yield was complemented by a significant reduction in the proportion of inappropriate samples donated to the WSBTS from 29% to 9.4%. Analysis of discard rates from two other units in the West of Scotland, one a District General Hospital and the other, a City Teaching Hospital identified cumulative discard rates of 18% and 10% respectively. In these units case selection was the responsibility of a Specialist Nurse from the WSBTS. This would suggest that having a dedicated individual responsible for patient recruitment may reduce the number of inappropriate allografts donated to the WSBTS.
Allogenic bone graft has proved valuable to a vast number of patients for the restoration of bone stock during revision arthroplasty surgery. The current shortage of allograft as a result of increased demand must be addressed until an efficacious and cost-effective synthetic alternative can be found.
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