Biomechanics and Orthopaedic Interventions



Head of Research: Dr. Jan Herman Kuiper

Orthopaedic interventions

Collaborators: Prof. James Richardson, Mr Joby John, Dr Mohammed Ali, Mrs Katherine Pitrolino, Dr Shailesh Naire

Patella fixation

Patella fractures make up about 2.5% of all fractures, the majority of these across the patella. The commonest fixation method is “tension band wiring”. In this method, two pins (“k-wires”) are first driven into the bone to keep the fragments aligned. A stainless steel wire is then wound around the bone in the form of a figure-of-eight, pressing the fragments together. Although this method is commonly used, it does have a high failure rate of around 20%.

A modification of the technique could help mitigate this failure rate. In the past, work from our lab has demonstrated that tension band fixation using an alternative figure-of-eight gives much stronger fixation of patella fractures (Fig. 1) [1]. Clinicians from the Department of Orthopaedic Surgery at Eulji University College of Medicine (Korea) adopted our technique and recently demonstrated that it gave better functional results at the early stage and reduced the complication rate [2].

Last year we showed that our alternative technique can be adapted to fix fractures of the olecranon (“funny bone”), drastically improving fixation strength. This year, we investigated if the technique could be improved further by looking at the influence of the diameter of the wire that is wound around the bone, and the number of wires used. These investigations were done on a model patella. Using this model, we were able to measure how much compressive force was generated between the two bone fragments and how well the construction could resist cyclic loading. Perhaps not surprising, there was a strong effect of wire diameter. Increasing the diameter from the standard 0.7 mm to 1.0 mm increased the amount of compression by 36% and reduced the amount of fracture displacement during cyclic loading by 49%. Further increasing the diameter to 1.2 mm had only a marginal effect, further increasing compression by only 7% and further reducing displacement by only 6%. Using two standard 0.7 mm wires proved not as effective as one 1.0 mm wire in terms of compressive force across the fracture - it increased compression by 17%. However, it did prove very effective in reducing displacement, managing to reduce it by 56%. We hope that these investigations will eventually lead to better patient care, not only in Korea but also in other places! 

Cell therapy for cartilage repair

Our hospital is at the forefront of the clinical use of cell therapy in orthopaedics. We are heading a number of clinical trials in this area, and have collected a large amount of clinical data. Cartilage defect patients are treated using Autologous Chondrocyte Implantation, whereby cartilage cells (chondrocytes) are isolated from a small biopsy and expanded in our OsCell cell manufacturing facility, eventually yielding between 1 and 20 million cells. These cells are implanted into the defect, after which they grow new cartilage. Growing new cartilage takes 1-2 years. One attempt to reduce this time makes use of a “scaffold”, a piece of very porous (typically 98%) material that is seeded with the cells. The idea is that distributing the cells throughout the defect will speed up the healing process and might even make better quality cartilage. However, a systematic review of clinical data found no evidence this strategy is successful.

To find out why, we used a mathematical model of a healing cartilage defect following implantation of chondrocytes [3]. This model takes into account such phenomena as cell growth (proliferation), cell migration, production of cartilage and diffusion of nutrients, all expressed as mathematical equations. Using this model, we compared cartilage growth between implanted chondrocytes (ACI) and chondrocytes seeded in a scaffold that fills the defect. We found that a scaffold has surprisingly little influence at the rate of cartilage formation (Fig. 2). Scaffolds do indeed help to distribute the cells throughout the defect from the time of implantation. However, by producing tissue while they spread, implanted chondrocytes are also spread throughout the defect within months (Fig. 2). The time-consuming part of the repair process is producing mature tissue, and this takes a long time regardless whether a scaffold is present or absent.

1. John J, Wagner WW, Kuiper JH. Tension-band wiring of transverse fractures of patella. The effect of site of wire twists and orientation of stainless steel wire loop: a biomechanical investigation. Int Orthop. 2007 Oct;31(5):703-7.

2. Lee, S. K., Y. S. Hwang, and W. S. Choy. "Horizontal versus vertical orientation of the loop for tension band wiring of transverse patella fractures." Orthopedics 37.3 (2014): e265-71.

3. Lutianov, M., Naire, S., Roberts, S., & Kuiper, J. H. (2011). A mathematical model of cartilage regeneration after cell therapy. J Theor Biol, 289, 136.


Statistical advice

Collaborators: Prof. James Richardson, Mr Sudheer Karlakki, Dr. Catherine Whittall, Mr Nigel Kiely, Mr Steve White, Mrs Sharon Roberts, Dr Naomi Dugard, Dr. Karina Wright, Prof. Sally Roberts,

This year continued the trend from the past years seeing our department put more effort into statistical advice than biomechanical experiments or mathematical models. This year’s most important work for clinical practice involved the analysis of a randomized clinical trial of arthroplasty patients, organized at the RJAH Orthopaedic Hospital. The trial aimed to find out if negative pressure wound treatment (NPWT), a method using a vacuum wound dressing to draw fluid from wounds and increase blood flow, would reduce wound complications and hospital stay of patients who received a knee or hip replacement. The trial found that hospital stay was indeed shorter if accounting for other factors also influencing stay. In addition, the complication rate was shorter.

A second important finding from our analyses involved data around cell therapy. We derived a risk score that surgeons can use pre-operatively to inform cartilage patients about their eventual risk of knee arthroplasty. In addition, our advice helped to understand why some knee patients have high levels of a cartilage-degrading enzyme (aggrecanase) and how reliable a score is that our hospital uses to assess children with upper limb problems.


Pilot study to evaluate negative pressure wound therapy in high-risk patients undergoing foot and ankle arthrodesis

Study progress

To date, since Trust approval was obtained, 90 patients have been screened for the study.  Of those, 65 have been deemed ineligible (mainly due to them not being classed as “high risk”).  Of the remainder, 14 patients have so far been recruited and randomised into the study.  11 of the 14 patients have had their surgery, with the first 10 patients successfully completing the study.

The patients recruited so far have included the following patients:


High Risk Factors


Multiple TMT joint fusion

Long-term steroid and aspirin

Fusion of 2nd and 3rd TMT joints                                 

Insulin dependent diabetes

Fusion of multiple TMT joints

BMI over 30

Talonavicular and calcaneocuboid fusion


Mid-foot fusion

BMI over 30

Ankle fusion

BMI over 30


Pantalar fusion


Talonavicular and calcaneocuboid fusion

BMI over 30

Ankle fusion

Smoker and BMI over 30

Talonavicular fusion

Inflammatory arthropathy, tupe ii diabetes and smoker

Ankle fusion

Long-term warfarin

Talonavicular and navicularcuneiform fusion

Long-term warfarin

Pantalar fusion


Ankle fusion

Long-term steroid therapy



All 11 patients are recovering well and so far there have been no major complications in either group.  The patients are followed up by both the consultant and the research team at 2 weeks, 6 weeks, 3 months and 6 months post-op with the PICO group attending at 1-week to have their PICO dressing changed.  At each visit the wound is assessed by the consultant and medical photographs are obtained.  There have been no readmissions and no issues with wound healing so far.


Fused Ankle Shoe (FAST) Study

Mr Patrick Laing, Dr. Caroline Stewart, Victoria Kidgell, Antonia Isaacson, Dr Sarah Turner, Dr Kirsty Davies, Megan Hyne, Julia Kennedy & Jenny Hunt.

Funded by the Orthopaedic Institute Ltd

FAST is a study to see if commercially available ‘rocker shoes’ (Figure 1) can be of benefit to patients who have had their ankle fused (arthrodesis).  Ankle fusion can be necessary following trauma or osteoarthritis and leaves the patient with an altered gait.  A normal walking stance phase has three stages, if the ankle joint is fused then the second stage (ankle rocker) cannot occur and the patient is forced to modify their gait to continue walking.  This can have a big impact on the patient as the modified gait can cause pressure to be exerted on other areas which can lead to further problems.  One can compensate for the loss of the ankle rocker by modifying the patient's footwear to incorporate a 'rocker sole', such as is done by NHS orthotic departments.  FAST uses gait analysis to look at how much different footwear can ‘normalise’ gait after ankle fusion.


 Figure 1: Typical commercially available "rocker" shoes, Skechers Shape-ups (left) and MBTs (right)

To date, 14 participants have been assessed; 11 males and 3 females. Ten have previously undergone an ankle fusion and 4 have undergone fusion of the ankle plus the subtalar joint, another joint in the foot. NHS ‘rocker’ soles had been prescribed for six participants although not all had followed through with the prescription; in total five participants had experienced wearing rocker soles, some of these individuals had tried out the commercially available rocker shoes themselves.

We have found that male participants, when wearing the commercially available Sketchers and MBTs were generally able to achieve a step length closer to that of an individual without a fused ankle. Walking speed and stride length were increased when wearing all shoes with the rocker soles compared to barefoot, with the fastest walking speed achieved with the commercially available shoes (Figure 2). Since the participants were able to walk with a longer stride length, the resulting walking speed was increased despite no change in the number of steps per minute (cadence).

Results were a lot more variable for the female participants and since only 3 female participants have been assessed, it is more difficult to draw accurate conclusions.

Most participants found the MBT and Skechers quite strange to walk in, taking some time to get used to with some participants feeling quite unstable. The majority of participants however confirmed that they were able to walk better with the rocker soles.

The data we have collected would suggest that the rocker shoes, including those available commercially, assist the participant to ‘normalise’ their gait such that less ‘abnormal’ pressure is exerted on their joints thus rocker soles may prevent additional joint related problems arising.

We have also measured the pressure distribution through the feet as the participants walk in each shoe type and will soon be analysing this data.

 Figure 2:

Spatial temporal parameters for male participants.  All measurements are compared to ‘normal’ barefoot walking patterns of healthy individuals (data previously collected from gait lab).