Evolution of Implants for Trochanteric Fracture Fixation: The Engineer's Point of View

Transcription

1 CHAPTER 4.7 Evolution of Implants for Trochanteric Fracture Fixation: The Engineer's Point of View H. Mçller-Daniels Trochanteric Intramedullary Fixation Devices More than 65 years ago, in November 1939, Gerhard Kçntscher implanted his first intramedullary nail in a shipyard worker who had fallen off the dock and broken his femur. This implant had been developed by Kçntscher and manufactured by Ernst Pohl in Kiel, Germany. This initial treatment was the beginning point for the breakthrough of closed intramedullary nailing, which today is accepted as ªstate of the artº in fracture treatment. Starting with this initial experience, Gerhard Kçntscher was constantly refining and improving the implants. He was constantly working on new ideas for implants to treat more and more different types of fractures. For the treatment of proximal femur fractures he developed the Y-nail in At that time Kçntscher recognized that intramedullary fracture fixation in proximal thigh bones significantly improves the biomechanical stability in comparison to a conventional side plate construct. This was due to the Fig Biomechanical advantage of intramedullary fixation versus extramedullary fixation shorter lever arm, as measured by d<d, especially in terms of load-bearing (Fig ). Nowadays side plates are called compression hip screws (CHS); the majority of them were not designed for the treatment of unstable proximal and subtrochanteric femur fractures and allowing full weight-bearing postoperatively. Treating these types of fractures with CHS as they were developed by McLaughlin in 1947 or Pohl in 1950 very often led to implant failures due to biomechanical overload. The dynamic hip screw, invented by Synthes in 1980, also did so [17±20]. Dr. Grosse at CTO in Strasbourg, France, as well as Dr. Halder and Mr. Gill in Halifax, UK, further developed in parallel and independent from each other the idea of intramedullary fixation at the beginning of the 1980s. After both designs were finalized in the Gamma nail, the so-called standard Gamma nail (SGN) was launched in 1988 (Fig a). This was the first intramedullary hip fracture fixation device allowing full weight-bearing because of its strong implant design. That is why it was able to treat all stable and unstable as well as ipsilateral and pathological femur fractures. Clinical support for the Gamma nail was given by A. Grosse and G. Taglang from CTO, Strasbourg, France, from the beginning. Since the market introduction the product range was completed by long Gamma nails and special nail shapes for the Asian population, the so-called AP and AP-J Gamma nails. In 1997, the second-generation nail, the trochanteric Gamma nail (TGN), was launched (Fig b). Its design was based on 9 years of clinical experience with the SGN. The TGN was improved by shortening the nail by 2 cm and reducing the medial±lateral bend from 108 to 48. These changes led to an optimized shape of the nail and to an even better clinical outcome [9±15] of the implant. More than 750,000 Gamma nail implantations have been performed so far. This seems to be very clear evidence that this is the right direction for intramedullary treatment with Gamma nails [1±8] in trochanteric fracture fixation. In 2001, a full range of tita-

2 140 H. Mçller-Daniels Fig Three generations of the Gamma nail: a SGN, 1988; b TGN, 1997; c Gamma3, 2004 Fig Finite element analysis to reduce the proximal nail diameter nium implants was launched under the name of Dyax-Asiatic and Gamma-Ti, mainly in Japan and Europe, to address surgeons' needs. The concept of the Gamma nail has been copied by more than 20 orthopedic companies during the past decade. After more than 15 years of clinical experience, the development of the third generation of Gamma nails started in the year 2001 with the contribution of leading surgeons of the AIOD and other trauma associations. Benchmarking the clinically successful TGN, the targets for the third genera-

3 Chapter 4.7 Evolution of Implants for Trochanteric Fracture Fixation: the Engineer's Point of View 141 Fig Strength improvement groove (left) tion of Gamma nails, the so-called Gamma3 nail system (Fig c), were as follows: Minimally invasive approach Offer lag-screw options for broader indications Develop operating room time-saving instruments. The engineering part of the design of the new Gamma nail generation was clearly defined. These three major points gave the engineers of Stryker a difficult time to reach their target: minimizing the diameter of the implants without compromising the strength and the cut-out resistance of the implants and developing instruments to allow minimally invasive surgery. Thanks to the support of high-end computeraided finite element analyses programs (Figs and 4.7.4) and intense biomechanical dynamic laboratory testing, it was possible to reduce the proximal diameter of the nail to 15.5 mm, providing the same strength as the current 17-mm TGN. The patented shape of the strength improvement groove (Fig ) was the main factor allowing minimization of the proximal part of the nails. The new implants of the Gamma3 nail system allow removal of approximately 16±20% less bone from the trochanteric region than other proximal femur nails with a proximal diameter of 17 mm and larger. The Gamma3 nails are available in three neck shaft angles: 1208 for coxa vara, 1258 as standard nail angle and 1308 for coxa valgus indications. The diameter of the lag screw was minimized to 10.5 mm, at the same time increasing the cutout resistance. This ambitious goal was realized because of the newly designed thread of the lag screw (Fig ) and verified by extensive biomechanical testing (Fig ), which confirmed the high cut-out performance. However, minimally invasive surgery is not only related to the implant size ± instruments also Fig New Gamma3 lag-screw geometry play a big role in reaching this goal. The new generation of Gamma3 instruments work perfectly together with the implants (results of early product surveillance). They allow small skin incisions for implantation, which lead to less blood loss and less risk of infections (Fig ). The instruments offer options for personal surgeons' preferences; the fragment control clip will provide additional fragment stability of the femoral head, for example (Fig ). That will stabilize the femoral head during lag-screw hole preparation and insertion, in cases of unstable and short head±neck fragments.

4 142 H. Mçller-Daniels Fig Gamma3 targeting device plus fragment control clip Fig Set-up for dynamic cut-out testing Fig Omega2 hip plate with twin hook fixation Trochanteric Hip Screw Devices Fig Gamma3 targeting device Development in the CHS segment is not standing still either. In order to allow smaller incisions for treatment with CHS in stable situations, a new cephalic device was developed (Fig ). This new implant option was developed in Sweden and is called twin hook. It allows plate implantation before the cephalic part follows. Therefore it avoids rotational forces to the femoral head and provides additional rotational stability when it is implanted.

5 Chapter 4.7 Evolution of Implants for Trochanteric Fracture Fixation: the Engineer's Point of View 143 A big clinical advantage of this design is the minimal invasive approach of the hip plate insertion because the plate can be implanted before the twin hook is placed. Even in cases of postoperative complications, the twin hook can be removed without removing the plate. Clinically the twin hook is also used successfully in combination with the Medoff plate [16]. Navigation in Trochanteric Fracture Fixation Fig X-ray of Omega2 hip plate with twin hook fixation Navigation in trauma treatment is becoming increasingly important. A more precise implant placement improves surgical accuracy in order to minimize failure and complication rates. Especially in trochanteric fracture treatment, navigation will allow reduction of: X-ray exposure to surgeon and patient Cut-out rate, due to exact lag-screw placement and entry point determination Soft tissue damage, due to exact prediction of incision point Size and number of mechanical guidance instruments. Furthermore it supports young and inexperienced surgeons in their training. Due to the above-mentioned clinical advantages, navigation will play a much bigger role in terms of fracture treatment in the very near future. Prospects Fig Twin hook: left delivery status; right expanded hooks The twin hook consists of two parts, an inner sliding tongue and an outer pin, which is 9 mm in diameter and compatible with the Omega2 hip plate. Fixing the twin hook in the femoral head is achieved by pushing the inner sliding tongue out through the proximal windows using a simple insertion device. By curling round and out about 10 mm on each side, the hooks give a durable fixation in the femoral head (Figs and ). Evolution never stands still. Requests regarding product improvements and cost reductions in total patient care and treatment arrive nearly daily from the clinical and the economic side. Fracture treatment should be done in a way that ensures security and is cost-effective. Fracture treatment is expected to be done simply and fast using excellent working implants and instruments, while postoperative complications related to this and surgical techniques have to be reduced to a minimum. Today most of the implant systems work mechanically with fixed guided instruments and target devices for the locking procedure. Therefore one of the most requested instruments for combined trochanteric and shaft fracture treatment is a reliable distal locking system for long nails. This device should also reduce X-ray exposure. A very promising distal targeting system will be available for the newest Gamma3 nail generation.

6 144 H. Mçller-Daniels: Chapter 4.7 Evolution of Implants for Trochanteric Fracture Fixation: the Engineer's Point of View Navigation systems are evolving fast. In future trauma surgery they will allow the surgeons much better orientation and visualization of the anatomic situation. Another breakthrough in the treatment of fractures will come with the further introduction of bioresorbable implants. Bioresorbable materials are going to become stronger and stronger. These new implants will probably take over a wide range of fracture treatment from conventional metal implants to bioresorbable implants. This may pave the way for further developments in the twentyfirst century. References 1. Parker MJ. Failure of femoral head fixation: a cadaveric analysis of lag-screw cut-out with the gamma locking nail and the AO dynamic hip screw. Injury 1998; 29 (7): Haynes RC, Poll RG, Miles AW, Weston RB. Failure of femoral head fixation: a cadaveric analysis of lag screw cut-out with the gamma locking nail and AO dynamic hip screw. Injury 1997; 28 (5/6): 337± Leung KS, So WS, Shen WY, Hui PW. Gamma nails and dynamic hip screws for peritrochanteric fractures. A randomised prospective study in elderly patients. J Bone Joint Surg Br 1992; 74 (3): 345± Guyer P, Landolt M, Eberle C, Keller H. The Gamma nail as a resilient alternative to the dynamic hip screw in unstable proximal femoral fractures in the elderly. Helvetica Chirurgica Acta 1992; 58 (5): 697± Guyer P, Landolt M, Keller H, Eberle C. The Gamma nail in per- and intertrochanteric femoral fractures ± alternative or supplement to the dynamic hip screw? A prospective randomized study of 100 patients with perand intertrochanteric femoral fractures in the surgical clinic of the City Hospital of Triemli, Zurich, September 1989±June Aktuelle Traumatologie 1991; 21 (6): 242± Dujardin FH, Benez C, Polle G, Alain J, Biga N, Thomine JM. Prospective randomized comparison between a dynamic hip screw and a mini-invasive static nail in fractures of the trochanteric area: preliminary results. J Orthop Trauma 2001; 15 (6): 401± Mockwitz J, Ernst S. Operative Versorgung per- und subtrochantårer Femurfrakturen ± Gammanagel oder dynamische Hçftschraube? Osteosynthese International 2001; 9: 211± Haynes RC, Poll RG, Miles AW, Weston RB. An experimental study of the failure modes of the gamma locking nail and the AO dynamic hip screw under static loading: a cadaveric study. Medical Engineering Phys 1997; 19 (5): 446± Lyddon DWJr. The prevention of complications with the Gamma locking nail. Am J Orthop 1996; 25 (5): 357± Friess P, Rader L. The Gamma nail. Indications, technique and early results. Zentralblatt fçr Chirurgie 1992; 117: 132± Hotz TK, Zellweger R, Kach KP. Minimal invasive treatment of proximal femur fractures with the long Gamma nail: indication, technique, results. J Trauma 1999; 47 (5): 942± Hotz TK, Breitenstein S, Di Lazzaro M, Keach KP. Trochanteric Gamma nail: a prospective clinical study on the treatment of peritrochanteric femoral fractures. OTA sat.10/20/01, Pelvis/Geriatrics, Paper #66, 11,30 AM; 179± Rosenwasser MP, Sinicropi SM. Proximal femoral fractures. Orthopedic Special Edition, Vol. 6, Bruce H, Ziran MD, Klatt B, Darowish M. Outcomes of Gamma nail fixation for peritrochanteric femur fractures. html 15. Karich B. Probleme mit dem y-nagel ± Optimierungsmæglichkeiten, Trauma und Berufskrankheit 2003; 5 (Suppl 2): S175±S Olsson O. Alternative techniques in trochanteric hip fracture surgery. Clinical and biomechanical studies on the Medoff sliding plate and the twin hook. Acta Orthop Scand 2000; 295 (Suppl): 1± Landolt M. Comparison and presentation of technique and results of the Gamma nail and dynamic hip screw. Helvetica Chirurgica Acta 1993; 59 (5/6): 965± Flahiff CM, Nelson CL, Gruenwald JM, Hollis JM. A biomechanical evaluation of an intramedullary fixation device for intertrochanteric fractures. J Trauma 1993; 35: 23± Haynes RC, Poll RG, Miles AW, Weston RB. An experimental study of the failure modes of the Gamma locking nail and the AO dynamic hip screw under static loading: a cadaveric study. Medical Engineering Phys 1997; 19 (5): 446± Leung KS, So WS, Shen WY, Hui PW. Gamma nails and dynamic hip screws for peritrochanteric fractures. A randomised prospective study in elderly patients. J Bone Joint Surg Br 1992; 74 (3): 345±351.