Most orthopaedic procedures involve using saw-blades for cutting bones either during arthroplasty or for performing osteotomy and re-alignment procedures. In the past, manual and gigli type of saws were used. This has now been replaced by the use of pneumatic and electric saws. Significant refinements in the manufacture and design of saw-blades were made over the years to improve the precision and reduce side effects of bone cutting. Despite advancement in the bone cutting process, many adverse effects are possible. Our article aims to provide an understanding of the issues relating to use of saw-blades and how to minimise these adverse effects.
When using saw-blades the effects to consider are:
1. Heat generation
Friction can generate significant heat. The thermal threshold for cellular injury is time dependent. Eriksson et al1 tested the effect of temperature on osseous cells using a dividable titanium implant that, after insertion in the tibial metaphysis of an experimental animal, permits numerical estimation of in-growing bone which was used to evaluate the effects of a defined temperature rise on bone regeneration. Heating the test implants to 47°C or 50°C for one minute caused significantly reduced bone formation in the implants, while no significant effects were observed after heating to 44 degrees C for one minute. The results reflect the importance of controlling the heat produced during surgery to avoid impaired bone regeneration.
From their work, two questions arise. Firstly, does osseous tissue attain such temperatures during orthopaedic operations and, if so, which procedures? Secondly, does such high temperature last that long?
One of the most thermogenic events in arthroplasty is bone cementation. Original work by Toksvig-Larsen et al2 showed that in cemented total hip replacement the cement bone interface temperature at the femoral side can reach 40 (29-56)°C, with acetabular side reaching 43 (38-52)°C even with pre-cooled cement. It is likely for the peak temperatures to last over a minute during the curing process.
Potentially higher temperatures can be generated during total knee arthroplasty. Larsen S et al3 demonstrated that bone cement interface temperature during cement curing reaches to 37 (31–50)°C with much higher temperature generated in the saw blade cutting the tibia side reaching 68 (45-100) °C and, more importantly, relatively high temperature generated of 47°C and 43°C at 2mm and 3mm depths of tibial bone cut. Interestingly, they showed that saline irrigation during cutting has only minimal effect on temperature.
It is the author’s opinion that one of the most common scenarios of generating high temperatures would be cutting through a good quality bone during re-alignment osteotomy e.g. high tibial osteotomy in a young patient and cutting through the subchondral sclerotic bone during knee arthroplasty. Therefore, sustained high temperatures exceeding one minute can be generated during such procedures. This can potentially affect bony integration onto the implant reducing longevity, though there is no direct evidence available in the literature to describe that.
Among various professions, electric and pneumatic hand-held saws generate vibration. Cumulative effect of that can be a health hazard. Guidelines from the European Vibration Directive relate the magnitude of vibration with duration of exposure a day. An interesting study by Roberts S et al4 showed that there are significantly higher self-reported upper limb sensori-neural symptoms in the form of finger numbness and tingling among orthopaedic surgeons when compared to gynaecologists. Multiple logistic regressions were carried out to compare the prevalence of these symptoms while adjusting for potential confounding factors which were not clearly controlled for in their previous similar study. However, it remains difficult to solely blame the use of saws during orthopaedic surgery as being the direct cause. This study also showed that orthopaedic surgeons are more likely to use vibration tools outside work (DIY; etc).
From available online resources, we know that the amount of vibration using large industrial tools and length of daily use is significantly higher than that generated whilst sawing bones during orthopaedic surgery. Nevertheless, further assessment of long term cumulative effect of the use of vibration tools by orthopaedic surgeons is needed to give a conclusive answer as it represents a potential hazard.
High levels of noise can harm hearing ability and affect speech discrimination. Noise effect is probably an underestimated subject in orthopaedic surgery. Several studies looked at this hazard but the most notable one is from Johns Hopkins Hospital5 where they measured background theatre noise, average equivalent noise and peak level frequency, each categorised for speciality. Among all specialities, orthopaedic theatres generated the highest level of noise, with an average equivalent to 66dB and peak level frequency exceeding 100dB in over 40% of times. More importantly, peak levels found routinely to be in excess of 120dB which is dangerous, particularly for children.
Guidelines for work place noise published by Health and Safety Executive (HSE) indicate that noise of average equivalent of 70dB or less will not cause hearing impairment in the large majority of people. Peaks of up to 140dB are also acceptable for adults at work and 120dB for children. Acute transient hearing loss is associated with noise above 110dB. Only acceptable noise
levels in hospital wards were published in these guidelines (of 30-45dB) with no specific guidelines about theatre level of noise being mentioned.
A study on noise level by power tools during orthopaedic surgery by Love H6 also supported that the overall noise level is within acceptable limits according to guidelines. However, peak levels (measured in his work to be over 140dB on multiple occasions during surgery) is a noise hazard and carries a significant, but unquantified risk for noise-induced hearing loss. Similarly, Siverdeen et al7 found that the noise generated during routine orthopaedic surgery was often significantly higher than the UK safety guidelines. Elderly patients have age-related hearing problems and the lack of the protective effect of their stapedial reflex to noise due to anaesthetic-induced paralysis can potentially result in further hearing loss. They recommend hearing protection, particularly to this group of patients as well as Orthopaedic staff who are regularly exposed to high peak noise. Conversely, Ullah R et al8 showed that despite recorded sound levels for instruments ranging from 119.6dB at source to 73.1dB at three metres, the exposure frequency is not great and hence the intermittent nature of exposure to the intense noise may protect staff against hearing loss, speech discrimination difficulties and tinnitus.
Reviews of the literature did not conclusively confirm that noise generated during orthopaedic surgery is a direct cause of hearing loss or speech difficulties to theatre staff. A very high level of noise is probably not routinely experienced in orthopaedic theatres and hence may not be a direct hazard to patients and theatre attendees. However, no well controlled study is available to reflect on the cumulative effect of noise levels generated during orthopaedic procedures and similarly for the effect of frequent high-pitch noise commonly detected during various procedures. In summary, noise generated during orthopaedic surgery represents another potential hazard that needs future research.
4. Metal debris and cut errors
Imprecise cuts due to blade design, cutting block slot design or operator errors can have detrimental effects. Cutting errors will affect implant alignment which can have disastrous long-term effect. Metal and bone debris generated during cutting can act as third body causing accelerated wear. Careful and skilful handling of saws along with using saw blades of appropriate thickness and design with appropriately matched jig slots will reduce these problems.
Therefore, an ideal saw-blade would be one that provides accurate bony cuts without generating too much heat, noise and vibration. All orthopaedic surgeons and trainees should be aware of these effects when choosing saw-blades for their procedures.
Authors would like to acknowledge Stryker® Cutting Academy for the supply of resources for this article.
- Eriksson RA, Albrektsson T., Effect of heat on bone regeneration: an experimental study in the rabbit using the bone growth chamber. J Oral Maxillofac Surg. 1984 Nov; 42 (11):705-11.
- Toksvig-Larsen S, Franzen H, Ryd L., Cement Interface Temperature in Hip Arthroplasty, Lund University Hospital, Department of Orthopedics, Sweden, Acta Orthop Scand. 1991 Apr;62(2):102-5.
- Larsen ST, Ryd L., Temperature Elevation During Knee Arthroplasty, Lund University Hospital Department of Orthopaedics, Sweden, Acta Orthop Scand. 1989 Aug;60 (4):439-42.
- Roberts SC, Harrild K, Mollison J, Murphy E, Ashcroft GP, Department of Orthopaedics, University of Aberdeen, Polwarth Building, Foresterhill, Aberdeen AB25 2ZB, UK, Occup Med (Lond). 2007 Mar; 57(2):104-11. Epub 2006 Dec 6.
- Kracht JM, Busch-Vishniac IJ, West JE, Noise in the operating rooms of Johns Hopkins Hospital, J Acoust Soc Am. 2007 May;121(5 Pt1):2673-80.
- Love H, Noise Exposure in the Orthopaedic Operating Theatre: a Significant Health Hazard, ANZ J Surg. 2003 Oct; 73(10):836-8.
- Siverdeen Z, Ali A, Lakdawala AS, McKay C., Exposure to noise in orthopaedic theatres – do we need protection?, Int J Clin Pract. 2008 May 28.
- Ullah R, Bailie N, Crowther S, Cullen J. Noise Exposure in Orthopaedic Practice: Potential Health Risk, J Laryngol Otol. 2004 Jun; 118(6):413-6.