Biomechanical study of dynamic changes in L4-L5 foramen surface area in flexion and extension after implantation of four interspinous process devices.
BACKGROUND
Lumbar spinal stenosis is a major public health issue. Interspinous devices implanted using minimally invasive techniques may constitute an alternative to the reference standard of bony decompression with or without intervertebral fusion. However, their indications remain unclear, due to a paucity of clinical and biomechanical data. Our objective was to evaluate the effects of four interspinous process devices implanted at L4-L5 on the intervertebral foramen surface areas at the treated and adjacent levels, in flexion and in extension.


METHODS
Six fresh frozen human cadaver lumbar spines (L2-sacrum) were tested on a dedicated spinal loading frame, in flexion and extension, from 0 to 10 N·m, after preparation and marking of the L3-L4, L4-L5, and L5-S1 foramina. Stereoscopic 3D images were acquired at baseline then after implantation at L4-L5 of each of the four devices (Inspace(®), Synthes; X-Stop(®), Medtronic; Wallis(®), Zimmer; and Diam(®), Medtronic). The surface areas of the three foramina of interest were computed.


RESULTS
All four devices significantly opened the L4-L5 foramen in extension. The effects in flexion separated the devices into two categories. With the two devices characterized by fixation in the spinous processes (Wallis(®) and Diam(®)), the L4-L5 foramen opened only in extension; whereas with the other two devices (X-Stop(®) and Inspace(®)), the L4-L5 foramen opened not only in extension, but also in flexion and in the neutral position. None of the devices implanted at L4-L5 modified the size of the L3-L4 foramen. X-Stop(®) and Diam(®) closed the L5-S1 foramen in extension, whereas the other two devices had no effect at this level.


CONCLUSIONS
Our results demonstrate that interspinous process devices modify the surface area of the interspinous foramina in vitro. Clinical studies are needed to clarify patient selection criteria for interspinous process device implantation.


METHODS
Level IV. Investigating an orthopaedic device.
Department of Orthopaedic Surgery, hôpital de la Pitié-Salpêtrière, AP-HP, UPMC University, 75013 Paris, France. Electronic address: carohirsch@yahoo.fr.
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Hirsch
Laboratoire d'anatomie, Université de Poitiers, 15 rue de l'Hôtel Dieu, TSA 71117, 86073 Poitiers Cedex 9, France.
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Breque
Clinical Investigation Centre, Poitiers University, Poitiers, France.
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Ragot
Department of Orthopaedic Surgery, hôpital de la Pitié-Salpêtrière, AP-HP, UPMC University, 75013 Paris, France.
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Pascal-Mousselard
Anatomy Department, Poitiers University, Poitiers, France.
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Richer
Anatomy Department, Poitiers University, Poitiers, France.
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Scepi
Department of Orthopaedic Surgery, hôpital de la Pitié-Salpêtrière, AP-HP, UPMC University, 75013 Paris, France.
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Khiami
D000368:Aged; D000369:Aged, 80 and over; D001696:Biomechanical Phenomena; D002102:Cadaver; D019299:Decompression, Surgical / Q000295:instrumentation; D006801:Humans; D021621:Imaging, Three-Dimensional; D008159:Lumbar Vertebrae / Q000503:physiopathology / Q000601:surgery*; D008422:Materials Testing; D011184:Postoperative Period; D019736:Prostheses and Implants; D011474:Prosthesis Design; D016059:Range of Motion, Articular / Q000502:physiology*; D012447:Sacrum / Q000503:physiopathology / Q000601:surgery*; D013123:Spinal Fusion / Q000295:instrumentation*; D013130:Spinal Stenosis / Q000175:diagnosis / Q000601:surgery*
Biomechanics; Interspinous process device; Lumbar spinal stenosis