This invention relates to fixation of objects to bone.
A variety of techniques are available for affixing objects, such as soft tissue, to bone. The oldest technique for affixing soft tissue to bone is to pass a thread through the bone and sew the tissue down to the bone. Many sizes, shapes and types of suture and needles are available to accomplish this task. Today, this method is still used for repair of tendons and ligaments in the hands of older osteoarthritic patients, although passing sutures through bone is generally difficult and tedious.
Venable et al. (1937), Annals Surg., Vol. 105, pp. 917-38, describes reactions of bone to metals, and recommends using Vitalium, an iron free and body fluid resistant alloy, for internal fixation devices, and particularly for screws. Prior to this publication, soft tissue repairs generally had been accomplished with string (suture), silver wires, or ivory pegs. Following publication of Venable et al., screws came into common surgical use, at first for repairing bone fractures, and later for attaching soft tissue to bone.
Vitalium staples were described for use in soft tissue repairs about 1940. Later many different types and styles of staple were suggested, including, for example, staples having four legs, or barbs in the legs, or various configurations of crossmember, including dentitions.
Metal implants, including implants made of stainless steel, are subject in time to corrosion and consequent loss of structure. Moreover, the presence of metal in an anatomical site can interfere with certain imaging diagnostic or therapeutic treatments near the site, such as magnetic resonance imaging; and where the use of such imaging is indicated, any metal implants may first have to be surgically removed. Patient sensitivity to free nickel ions in stainless steel implants has fueled a growing controversy regarding the use of materials containing high quantities of nickel, including nickel-titanium alloys such as Nitinol.
Generally, the tissues react to metal screws and staples as foreign bodies, and these objects can be expected to loosen in time as a result of rejection of them by the tissues. A loosened screw or staple can be expelled from the bone, and can lodge in a joint, where it can cause damage to articulating surfaces. In a significant proportion of cases, where the screw or staple has been expelled or has loosened, it must be removed in a subsequent surgical procedure.
Since the development of the stainless steel screw and staple, many small improvements have been made for fixing soft tissue to bone. In one improvement, described for example in Daniel et al., Chapter 8, In: Jackson et al. (1987), The Anterior Cruciate Deficient Knee, C. V. Mosby, pp. 114-126, a circular plastic washer with spikes on its undersurface is installed beneath the screw head to provide fixation without crushing the tissue, and toothed washer devices have been commercialized by, for example, A. O. Synthes, Switzerland. This method was until recently widely accepted as the best method of fixating soft tissue to bone, except in shoulder repair where sutures passed through holes drilled through the glenoid margin and through the edge of the glenoid capsule continue to be used for approximating the capsule to the glenohumeral rim, generally as described in Bankart (1983), British Jour. Surg., Vol. 26, pp. 23-39. Rowe et al. (1984), Jour. Bone Joint Surg., Vol. 66A, pp. 159-68, for example, describes using a Bankart procedure and in all instances avoiding the use of metal implants such as staples and screws in the vicinity of the shoulder joint.
Necrosis of the soft tissue can result if the tissue is too tightly clamped by screws or staples, and several attempts have been made recently to improve the soft tissue fixation by screws and staples to overcome this problem, such as by using toothed washers, as described above, or by using stand-off devices to prevent crushing the soft tissue. On the other hand, if the soft tissue is too loosely fixed to the bone, the holding power of the tissue attachment is inadequate to facilitate effective soft tissue reattachment to bone. Because it is almost impossible to adjust the compression exerted by screws and staples on soft tissue, these devices are not fully satisfactory for soft tissue repair. The surgeon's fondness for suture in soft tissue repairs has never diminished, owing primarily to the fact that, by setting the tension of the suture, the surgeon can fix the soft tissue to the bone as tightly as is appropriate in the particular case and according to the surgeon's practice.
Somers et al. (1985), U.S. Pat. No. 4,632,100, describes a cylindrical suture anchor having a drill formed at one end and flights of screw threads at the other end. The device combines a drill point for penetrating the hard outer cortical bone with a screw for fixing the device into the hard bone, providing for drilling the bone and installing the anchor in one operation. A Somers et al. device, marketed as STATAK.TM. by Zimmer, Inc. (Warsaw, Ind.), is screwed into a 4.5 mm diameter bone hole, and is intended to be countersunk into the cancellous bone to a depth up to 18 mm, and so it is not ideal for use in smaller joints. The relatively large size and the comparatively high cost of the device, and its requirement for a large hole in the bone, may be deterrent to its use, and it has not been well received.
Goble et al. (1986), U.S. Pat. No. 4,738,255 describes a suture rivet that can be inserted into and locked in place in a performed hole in bone. The initial pilot hole is cut using a drill having scissoring blades, so that the resulting hole is flared or skirted, having a greater diameter deeper within the bone than at the entry to the bone surface. The anchor itself includes a rivet and a slotted ring. The slotted ring, which passes the smaller entry hole, is inserted within the bone, and then the rivet is passed into the hole and through the ring, fracturing the ring at the point where it is slotted and flaring the ring so that it cannot pass out through the entry hole, locking the assembly into the bone hole. The Goble et al. apparatus is relatively complicated, and the scissoring device can be unreliable in use.
Gatturna et al. (1987), U.S. Pat. No. 4,898,156, describes a suture anchor assembly consisting of a titanium body affixed to a nickel titanium arc of wire. The nickel titanium arc is of pseudoelastic nitinol, which can be strained such that the arc will straighten completely, allowing the assembly to be placed into a predrilled bone hole. The titanium body has a drilled cross hole which allows a suture to be attached to the body prior to insertion in the bone hole. The installation tool consists of coaxially disposed cannulae, which constrain the nitinol arc prior to insertion.
Nicholson et al. (1987), U.S. Pat. No. 4,899,743, describes a suture anchor installation tool that holds the Gatturna et al. suture anchor so that the nitinol arc is unconstrained, essentially hanging outside the installation tool. Prior to insertion the assembly resembles a one barbed fish hook in the end of a small spear. A hole is predrilled in the bone, and the anchor assembly is gently pushed into the predrilled hole, allowing the nickel titanium arc to slide down the side of the hole. A Gatturna et al. anchor and Nicholson et al. installation tool, commercialized by Mitek Surgical Products, Inc., beginning in late 1989, have become a preferred method of anchoring soft tissue to bone; many were sold in the first year following FDA approval. The device can be effective in aiding in soft tissue reattachment, and has an advantage in requiring a relatively narrow hole in the bone.
However, the Gatturna et al. anchor is set by applying traction to the suture, and so the device does not lend itself to use as a rivet, in which no suture would be required to anchor the tissue. Moreover, use of the device is contraindicated in very soft, cancellous bone, as is typical of bone in many joints, so the device is not optimal for such procedures as rotator cuff repair, osteoarthritis joint reconstruction, and the like. When the Gatturna et al. anchor is deployed in an arthroscopic application using the Nicholson et al. installation tool, the protruding barb can engage sensitive tissues during placement and cause damage to the tissues.
Hayhurst (1988), U.S. Pat. No. 4,741,330, and international patent Publication No. WO 89/10096 describes a suture anchor including a generally bullet-shaped resilient plastic member having a rounded convex base from which legs extend. The legs, which are provided with outward-pointing barbs on their outer surface, diverge outwardly when the member is in a relaxed state. The member is compressed and inserted into a predrilled bone hole, and then allowed to relax, so that its resilience is said to urge the legs outward against the bone hole wall. The anchor supposed to be set by applying tension to the suture, causing the edges of the legs and the surface barbs to dig into the bone. A similar device, marketed by Acufex Microsurgical, is driven into the bone hole apparently into the cancellous bone, and is then set by pressing a spreader downward between the legs while pulling upward on the suture to force open the legs.
Bays et al. (1990), U.S. Pat. No. 4,924,865, describes a bioabsorbable tack for joining severed or torn soft tissues, such as cartilage. The stem of the generally T-shaped tack is hollow and covered with barbs on its outer surface. The tack is implanted by passing the stem through a hollow cylindrical applicator and passing a needle through the axial bore in the stem, then driving the needle, tack and applicator through the tissues to the desired depth, and then withdrawing the needle and applicator, leaving the tack in place.