What is in the Journals?

Saleh K et al. 

Symposium on operative treatment of patellofemoral OA. JBJS 87-A 3: 659-70.

The symposium on the latest issue of American JBJS addresses a very important clinical entity where understanding of the biomechanical principles is of the paramount need. OA of the PFJ is quite common and management is just as widely unsatisfactory. This is partly due to the poor understanding of the biomechanics of the PFJ. This article is the product of many leading practitioners coming together to present a unified front at the AOA meeting in 2004.

Detail discussion of anatomy or biomechanics was beyond the remit of the article and is not elaborated. The article discusses the rationale for the operative procedures practised for treating PFJ OA in a graded fashion, starting with soft tissue procedures, tibial tubercle osteotomy, chondrocyte transplantation, PFJ replacement and, finally, TKR. Each operation has a role to play in the treatment. The message one gets is that precise understanding of the biomechanical abnormality and careful patient selection is essential for success of treatment.

Hortobagyi T et al. 

Altered hamstring-quadriceps muscle balance in patients with knee osteoartiritis. Clin Biomech 20:97-104.

This article would be of interest to surgeons interested in physiotherapy as a mode of management in osteoarthritis. Various studies have shown that physiotherapy is a useful tool for treating early osteoarthritis of the knees. Physio mainly concentrates on quads build up exercise. In a non-randomised case control study, the authors show that quads-hamstrings muscle recruitment is altered in knee OA. Quad-hamstrings activity was tested with surface electrodes during level walking and stair climbing and descent. Hamstring muscle coactivity was found to be greater during ADL in OA subjects. That patients with knee OA have weak quads is well documented. However, studies in the past have not addressed the question of quads/hamstrings balance in OA. More importantly, the study also found that altered muscle response was more widespread than quads/hamstrings coupling and suggests that therapeutic interventions should not limited to strengthening quadriceps muscles but also target other lower limb muscles.

Rowe SM et al. 

Why does outer joint motion predominate in bipolar hip prosthesis? Acta Orthop Scand 2004; 75(6):701-7.

Bipolar hip replacement has been advanced as a viable option in young patients with displaced subcapital fracture of neck of femur. The theoretical premise is that a bipolar head, in contrast to a unipolar one, would allow movement at the inner joint and preserve the acetabulum to some extent. Further studies have yet to prove this assertion. However, this has not distracted surgeons from offering bipolar hip prosthesis to their patients. Latest refutation of their practice comes from Korea . The authors examined the motion distribution of bipolar cup by inserting bipolar prosthesis in fresh frozen cadaver pelvis and observing the motions under video. They also did a fluoroscopic study of 50 bipolar hips done at their centre in different movements with or without weight bearing. They found that although both inner and outer motion coexisted in most of the patients, outer motion was predominant in all directions of leg movement. The authors feel that this could possibly be due to two reasons: early impingement of femoral neck on the liner and increased lubrication of the outer joint. The authors feel that variable degree of valgus positioning of the human acetabular cup results in early impingement of the prosthetic neck on the liner and induce outer cup motion. The other explanation offered is that on weight bearing synovial fluid is pressed out of the inner joint and lodges inside the less congruent outer joint. The more lubricated outer joint encourages more movement.

Rodeo SA et al. 

What’s new in orthopaedic research?  JBJS A  86 A Sept 2004 pp. 2085-97.

Authors have described recent advances in orthopaedic research in specialty update section in the recent issue of JBJS A.

Cartilage degradation and repair:

Our understanding of cartilage degradation and repair is still limited. Recent studies have indicated that extracellular matrix proteins , when fragmented, may have deleterious effect on chondrocyte metabolism. Many of the pathways involved in this interaction are being identified.

Using drugs to manipulate fracture healing:

It appears that our experience of treating osteoporosis could lead to increasing understanding of ways to use drugs to manipulate fracture healing. Bisphosphonate is used to treat osteoporosis. It prevents bone resorption by inhibiting osteoclasts. This mechanism also delays bone remodelling. Conversely, use of parathyroid hormone enhances bone formation and may help in treating disuse osteoporosis  following trauma.

Use of NSAID following trauma:

There is concern that NSAIDs can impair fracture healing by inhibiting inflammation. Animal studies showed reversible impairment of fracture healing when COX 2 inhibitors were used. It is recommended that their short term use is safe in healthy patients but NSAIDs should be avoided in patients with risk factors-diabetics, those on steroids, smokers etc.

Alternate implants:

To date implants used in orthopaedic practice are designed to transfer load to host bone. New hydrogel implants are being developed which intend to act as load sharing device. Hydrogel is hydrophilic polymer. Candidates for use would be meniscus replacement, IV disc replacement etc. Animal studies have shown promising results. 

Tissue engineering:

One of the challenges of tissue engineering is to manufacture a tissue scaffold that can withstand in-vivo mechanical load and also allow biologic integration. The authors discuss studies that have  explored nanotechnology to build better scaffolds.

 V. Pinskerova; P. Johal; S. Nakagawa; A. Sosna; A. Williams; W. Gedroyc; M.A.R. Freeman

Does the femur roll-back with flexion?  Volume 86-B Number 6 August 2004, 925-32.

The answer is, yes, but not as we know , or we like to think we know it does. In this multi-centre study, Pinserova et al sets out to challenge this axiom of orthopaedic biomechanics. We are interested in the kinematics of the normal knee. Because that is what we would like to replicate in the prosthetic knee.

Femoral roll-back is a conceptual cornerstone around which controversy centres regarding modern design of total knee replacement. Proponents of PCL retaining prosthesis argue that keeping PCL helps to create nearer normal movement in the prosthetic knee. With increasing flexion, PCL tightens due to the four-bar rigid linkage mechanism which results in posterior roll-back of the femoral condyles and helps to give more ROM. However, studies comparing PCL retaining and sacrificing prostheses have not found this to be a significant factor.

The authors performed MRI scan on six cadaver knees and five living subjects during weight bearing squat and non weight bearing state to identify the relative position of the flexion facet centre of the two condyles and contact points at varying degrees of knee flexion. ( If you want to know what the flexion facet centre is you need to read another paper by the authors, which I have not yet read).Contact point was defined as the point at which medial and lateral subchondral plates of femur and tibia most closely approximated each other.

The study found posterior shift of contact points of both condyles in both living and cadaver knees , nullifying any possible role of muscular action. The PCL was never taut and could not have contributed towards a rigid linkage mechanism. The FFCs, on the other hand, moved differently. Lateral condyle moved backwards , but medial moved very little. The authors attribute this difference to the difference between the condylar articular shapes.

They conclude that femoral roll-back is a misnomer. There is posterior shift of the point of contact but the condyles essentially rotate externally with increasing flexion without any contribution from the PCL. 

Noyes FR, Barber-Westin SD, Rankin M. 

Meniscal Transplantation in Symptomatic Patients Less Than Fifty Years Old. J Bone Joint Surg Am 2004 86: 1392-1404.

A prospective review from Cincinnati on the results of meniscal transplantation in symptomatic young patients. 

That menisci are important for shock absorption and load dissipation is now well known.  Unfortunately, due to its poor vascularity very few menisci are amenable to repair. Partial or total menisectomy results in early OA. A successful transplantation would be a great boon for many of these patients. 

Noyes et al prospectively reviewed 40 allograft transplants in 38 knees. These were the result of sporting injuries.There was no control group. Patients with gross OA were excluded. Grafts were analysed pre and post transplantation by an independent observer with MRI .  Most of the patients had single meniscal graft. Quite a few also had osteochondral graft and/or soft tissue procedures. The reported success rate is modest ( more than 50% had abnormal allograft signal, 76% returned to light sports), the follow up is short ( mean 40 months). Lateral meniscal graft is known to have better survival rate. They do not mention the side.

It can be argued that improvement in knee score could be due to the other procedures. Authors agree that the study shows the results of short term symptomatic beneficial effects only. They also recommend early than late transplantation. This is on the presumption that early transplantation would have some chondroprotective effect. Biomechanically, this makes sense. 

Sadly, there are many unresolved issues with allograft. We do not know how meniscal allograft would respond to a different environment. Is there a  long term  chondroprotective effect ? Future long term studies can answer that question. For now immediate short term effects seem to be encouraging. 

Muschler GF, Nakamoto C, Griffith LG.

Engineering Principles of Clinical Cell-Based Tissue Engineering.  J Bone Joint Surg Am 2004 86: 1541-1558.

A review article from USA on the principles of tissue engineering, including current position and future promises for the muskuloskeletal system. The public perception of tissue engineering is limited to ex-vivo growth of new tissue and viable transplant in-vivo. Although we have not reached that stage as yet, research and development in this speciality has witnessed great strides. We learn about stem cell cycle, their  broad phenotypic potential, and present efforts to utilise them. We learn of present strategies to target stem cells and future promises. Technology has advanced to the stage where it is possible to harvest few stem cells and culture them to sufficient numbers to allow in vivo transplant. A major obstacle still is a viable scaffolding that would protect transplanted cells and allow them intended function. Optimum type of scaffolding remains unresolved. A major  emphasis in future is likely to be on modulation of local cellular environment. This could be a possibility with the use of viral vectors. 

Lin TW, Cardenas L, Soslowsky LJ. 

Biomechanics of tendon injury and repair. J Biomech. 2004 Jun;37(6):865-77. 

Type: review article 

Setting: University of Pennsylvania,  USA

Aims: To discuss tendon repair mechanisms, experimental animal models and current and future treatment modalities. 

Tendons serve important functions. They transmit large tensile forces between bone and muscle. They are also prone to injury. Commonly, they are injured at the musculo-tendinous or osteotendinous junction due to overuse or tensile overload. Healing is difficult due to poor vascularity and cellular paucity. We know that functional outcome after tendon injury depends on many factors. There are proponents of both intrinsic and extrinsic tendon healing. Intrinsic theory demands that tendon can heal on it's own from local blood supply without scarring. Extrinsic theory proposes local inflammation, scarring and external blood supply to be important for healing. The truth, probably, is somewhere in the middle. 

Natural history of tendon healing is with scar formation. This scar is biomechanically inferior to normal tissue. The gap has poor tensile strength and, if greater than 3 mm, does not improve over time. 

Repair strength of tendon is directly proportional to the no. of strands crossing a repair site. Additional epitenon suture gives better strength over core suture alone. 

Animal studies with activity have shown generally positive effect of exercise on tendon. Disuse has resulted in adhesion and poor functional property. Both active and passive motion of flexor tendons post-injury resulted in improved tensile property. 

Finally, the paper discuses future treatment options. Biocomposite materials have been tested to serve as replacement tissue or to enhance healing. They have not been found to fulfill the biomechanical requirement of original in vivo function. Cytokines have also been proposed, but the delivery system is not still developed. 

A new approach is functional tissue engineering (FTE). It intends to identify in-vivo functional requirement to design safer and more effective composite. 

New developments in molecular biology are likely to make cell therapy a possibility. Mesenchymal stem cells are likely candidates for tendon healing therapy. They can be isolated from bone marrow. Delivery system is again a problem and to date, studies have not showed marked difference in outcome. If the delivery system can be resolved, gene therapy could also become viable.