Minimally Invasive Total Hip Arthroplasty At Exeter
Introduction
In the last few years there has been an increasing interest in the application of minimally invasive surgery (MIS) techniques to the field of total hip arthroplasty (THA). Developments in surgical methods and instrumentation have allowed surgeons to reduce the length of incision through which the operation is performed. Although at the present time nomenclature and classification have not been finalised we use the term minimally invasive THA for any procedure in which the incision and surgical access are modified in an attempt to reduce the tissue trauma associated with hip replacement. Most authors who have reported results in this field have used a wound of 10 cm or less1-8, and this is emerging as the upper limit of incision length for MIS hip replacement. Several different techniques for MIS hip replacement have been described4-12, making it somewhat difficult to compare results between centers. The different techniques have recently been classified 13 into two main groups: the minimal approaches and the micro-minimal or two-incision approach. The minimal incision approaches are small-incision modifications of the standard posterior5, 6, 8, 9, 11, 12, anterolateral14 and anterior15 approaches used for THA. The Micro-minimal approach is a new development4 that utilizes intermuscular planes to gain access to the hip joint, and avoids the conscious detachment of muscles and tendons.
The underlying aim of MIS hip replacement has been to reduce the tissue trauma associated with THA, which it is hoped will confer benefits on both patients and health care providers, but unfamiliarity with the approaches also has the potential to increase complication rates, and this needs to be audited closely. In the sections below we set out the potential advantages and disadvantages that we believe MIS hip replacement may have over standard incision techniques, and which form the basis for on-going research being performed at Exeter on minimally invasive hip replacement.
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Potential Advantages for the Patient
A reduction in tissue trauma associated with hip replacement has the potential to reduce blood loss and transfusion rates, to reduce post-operative pain, to hasten recovery of normal function and to improve scar cosmesis.
Several authors have found a reduction in estimated blood loss associated with MIS hip replacement2, 5, 8, 10, 11, 14. However, the accuracy of estimated blood loss is open to question and post operative haemoglobin results after MIS hip replacement have either been no different14 or have even tended to be lower than in controls5. Di Gioia et al11 found that the mean transfusion requirement for MIS patients was 0.7 units, compared with 1.1 units for controls (p<0.05) and Wenz et al10 found a similar result. However, although these studies demonstrated a statistically different result, the clinical significance of these results is doubtful and two other studies5, 14 have failed to show any difference in transfusion requirements.
Several studies have demonstrated encouraging results in the recovery of function post-operatively. Wenz et al10 found that MIS patients ambulated significantly sooner in the postoperative period (p=0.02), but this study compared MIS posterior approach with a standard length incision anterolateral approach, and the recovery of ambulation may owe as much to the approach as to the incision. Chimento et al2 found that significantly fewer of their MIS patients limped at six weeks (p<0.04), DiGioia et al11 reported that patients had significantly higher Harris Hip Scores 3 months, and 6 months after mini-incision THA, although there was no functional difference between the two groups one year after surgery.
Despite the encouraging functional results in these three studies2, 10, 11 they failed to show any difference in the length of stay of MIS patients and controls. However, Wright et al3 found that the length of stay was less for their MIS patients (p<0.02) and Howell et al14 found a similar result, although in this latter study the patients differed significantly between the two groups with respect to their body mass indices. Swanson and Hanna8 found that MIS patients made a faster return to full activity (p<0.001), and Berger4, Dorr6 and Sherry12 have all reported favourable recovery of postoperative function with short lengths of stay but in each of these last three studies there was no control group for comparison.
One of the advantages of MIS techniques when applied to other branches of surgery is a reduction in the post-operative pain associated with an operation. Although this potential exists for hip replacement, there is relatively little in the literature to suggest that smaller incisions have led to a reduction in post-operative pain. In a randomized controlled trial of MIS versus standard incision THA, Chimento et al2 found no difference in the narcotic requirements of the two groups of patients. Swanson and Hanna8 compared a cohort of MIS hip replacement patients with historical control patients that had their surgery prior to the introduction of MIS techniques. They defined “problem pain” as deviation from their standard postoperative pain management protocol, and they found that no MIS patients suffered from “problem pain” compared to 12% of the control patients (p<0.001), but the use of historical controls in this study has the potential to introduce bias. Dorr6 has described in detail the pain and analgesia requirements of 90 patients undergoing MIS hip replacement, but without controls the results are difficult to interpret.
The cosmetic advantages to the patient are obvious and they may play a major role in the introduction of MIS hip replacement into widespread use, particularly in health care systems in which market forces apply. Three studies3-5 have reported the positive attitude of patients towards the scars that result from MIS hip replacement, and indeed one of these studies3 suggested that the cosmetic benefit may be the only clinical advantage of MIS hip replacement over standard incision techniques.
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Potential Advantages to Health Care Providers
The introduction of minimal incision methods into other fields of surgery has been associated with faster recovery times and a reduction in the length of hospital stay in the post-operative period. Surgeons face increasing pressure to reduce the costs of operations and the length of stay associated with each procedure16. If MIS hip replacement is associated with shorter hospital stay, then it is likely that increasing numbers of hip replacements will be done using smaller incisions.
Howell et al14 compared a group of patients who had hip replacement through a minimal anterolateral approach with a group of controls who had their hip surgery performed through a standard anterolateral approach. They found that the mean length of hospital stay for MIS patients was 4.4 days, compared to 5.7 days for control patients (p=0.03). This differs to the findings of three other studies2, 3, 11, which have shown no difference in the length of hospital stay, despite favorable recovery of function among MIS patients.
The orthopaedic literature is lacking in well-designed economic evaluations of different surgical strategies in total hip replacement17, 18, and the influence of length of stay on the total cost of hospital care associated with the operation is controversial. Healy et al19 have shown that almost 80% of the total hospital costs associated with the provision of THA are generated within the first 48 hours of admission; in the operating room, recovery room, pharmacy, and in postoperative nursing costs. In their study they found that the cost of the first hospital day accounted for 68.25% of the total costs, and these costs reduced dramatically during the subsequent days so that the 6th day of hospital admission accounted for only 2% of total costs. Therefore in order to have a major effect on the total costs of providing a hip arthroplasty service, MIS techniques will need to radically reduce hospital length of stay, and even then many of the costs will remain fixed. There are reports of day care hip arthroplasty 4, 20 using MIS techniques but this may not be achievable for the majority of hip replacement patients. Indeed the widespread introduction of day case hip replacement may increase referral rates to rehabilitation units, particularly for elderly patients, patients who live alone and those with comorbid conditions21.
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Potential Disadvantages of Minimally Invasive Hip Replacement
Hip replacement performed through standard length incisions has proved to be extremely successful in the long term, producing improvements in pain, function, mood, general health and quality of life22, 23. It is therefore a concern to orthopaedic surgeons that the introduction of MIS techniques may adversely affect the results of hip replacements, particularly of they lead to an increase in complication rates. Several studies2, 3, 5, 8, 10 have looked at complication rates following MIS hip replacement, and so far none of them has reported an adverse result. However, the follow up in these studies is short, and it is essential that complication rates be monitored closely as minimal incision techniques are introduced into widespread practice.
One of the potential drawbacks of minimally invasive techniques is the possibility that these techniques may lead to an increase in duration of each procedure13, which is to some extent dependant upon the type of MIS surgery undertaken. Using the two-incision technique there is an initial learning curve period, during which operative times exceeding four hours have been reported4, although with experience this figure can be substantially reduced. Chimento et al2 studied the operative time using the minimal posterior approach, and in their prospective randomised trial they found no difference in the mean operative time between MIS patients and controls. The results of several other studies3, 8, 10 support the results of Chimento et al, although in many of these studies there are significant confounding factors that favour the MIS patient group. The surgical time using the minimal anterolateral approach has been reported by the Vancouver group14, who published the results of their first 50 cases. They found that the mean operative time for MIS patients was 97 ± 19 minutes, compared to 84 ± 15 minutes for the control group (p=0.0001). This result is despite the fact that the MIS group in this study had a significantly lower mean body mass index, which could be expected to favour the operative time of the MIS patients.
The literature therefore has mixed results for the effect that minimally invasive techniques have had on operative times, and further studies are required to clarify this issue. If there is an increase in operating theatre time associated with MIS techniques this will have adverse health economic implications for the widespread acceptance of these techniques.
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Minimal Incision Research At Exeter
The surgeons on the Hip Unit at the Princess Elizabeth Orthopaedic Centre have been developing a surgical technique and instruments for the minimal posterior approach to hip replacement, using cemented acetabular and femoral components. They have been using these instruments and the minimal posterior approach for over one year, and the initial results have been good.
They are now embarking on a prospective randomised trial of MIS posterior approach versus a posterior approach using a skin incision of at least 15cm. Outcomes will include blood loss, post-operative pain, length of stay, functional score results, and the results will be published in due course.
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References
1.Sherry E, Egan M, Henderson A, Warnke PH. Minimally invasive techniques for total hip arthroplasty. J Bone Joint Surg Am 2002; 84-A:1481.
2.Chimento G, Pavone V, Sharrock N, Kahn B, Cahill J, Sculco T. Minimally invasive total hip arthroplasty: a prospective randomized study, 70th Annual Meeeting of the American Academy of Orthopaedic Surgeons, New Orleans, LA, Feb 2003.
3.Wright J, Crockett H, Sculco T, Lyman S, Madsen M. Mini incision for total hip arthroplasty - a prospective, controlled investigation with 5 year follow-up, 70th Annual Meeting of the American Academy of Orthopaedic Surgeons, New Orleans, LA, Feb 2003. Vol. Paper No. 277.
4.Berger R. The technique and early results of the two-incision minimally invasive total hip arthroplasty, Thirty-first Open Meeting of the Hip Society, New Orleans, Feb 2003.
5.Goldstein W, Gordon A, Branson J, Berland K. Minimal incision total hip athroplasty [Scientific Exhibit No. SE204], 70th Annual Meeting Proceedings of the American Academy of Orthopaedic Surgeons, New Orleans, 2003.
6.Dorr L. Mini-incision for THA: pros, cons and experience to date, Thirty-first open meeting of the Hip Society, New Orleans, 8th February 2003.
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13.Howell J, Garbuz D, Duncan C. Minimally invasive hip replacemement: Rationale, applied anatomy and instrumentation. Orthopedic Clinics of North America 2003; In press.
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19.Healy WL, Iorio R, Richards JA, Lucchesi C. Opportunities for control of hospital costs for total joint arthroplasty after initial cost containment. Journal of Arthroplasty 1998; 13:504-7.
20.Mathias JM. MIS total hip implant speeds recovery. OR Manager 2001; 17:5-7.
21.Forrest GP, Roque JM, Dawodu ST. Decreasing length of stay after total joint arthroplasty: effect on referrals to rehabilitation units. Archives of Physical Medicine & Rehabilitation 1999; 80:192-4.
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