Saw transection of retained compression screws with damaged heads instead of removal in revision first metatarsal osteotomy: a technique tip

Abstract

Distal first metatarsal osteotomy is performed to correct hallux valgus. The surgery is being performed throughout the UK in increasing numbers. The osteotomies used are commonly fixed with one or two variable pitch compression screws. Recurrence of the deformity or inadequate correction in the primary surgery may require revision osteotomy which necessitates removal of previous screws. Revision rates for scarf osteotomy have been reported at 5%. Removal of screws can be challenging as they are often buried in bone and/or the screw heads can get damaged even despite meticulous preparation. Various techniques for removal of damaged screws are described, which require additional equipment and may result in significant loss of the host bone. We describe another technique where a standard Stryker TPS sagittal saw and saw blade (Kalamazoo, USA) are used to cut through the shaft of the compression screws in line with the planned revision osteotomy. We have successfully performed this on two occasions with good results, and describe our experience of using this technique which eliminates the need for complex over drilling procedures often required for removing stripped and retained screws

Background

Removal of retained metal work is a common challenge in orthopaedic surgery.¹ This case is important because it offers a relevant, safe and simple solution to this problem faced by the orthopaedic community, and in this instance, foot and ankle surgeons specifically. Various techniques and tools for removing retained metal work have been described, for example, hollow reamers, reverse cutting screws, diamond tipped angle grinders, tungsten carbide drills, metal foil or cement interposition into stripped screw threads.

Our technique for removing stripped compression screws in delicate first metatarsal osteotomies, using a standard surgical grade stainless steel pen drive saw has not been described before. This technique showed itself to be safe, simple and effective in our experience. We feel it is important to share this information with the orthopaedic and foot and ankle community.

Case presentation

The patient is prepared as for a standard first metatarsal osteotomy. Screw removal sets need to be available and these must include the appropriate sized reverse cutting screw extractor bits as well as crown drills for overdrilling. A selection of narrow osteotomes and small curettes for removing bone over growth and exposing the screw heads are essential. Image intensification may also be necessary to locate buried screws. The procedure is as for the routine revision surgery. The screws are identified and the heads are cleared from all bone using osteotomes and small curettes, taking care not to damage the metal, but at the same time clearing out the entire rim of the screw head from overgrown bone. The appropriate cannulated screw driver is then engaged using a guide wire to ensure an inline engagement between the screw and the screw driver. The screw is then turned with utmost care to prevent stripping. Depending on the force required, it is possible to strip the screw head threads before removal is complete. Reverse cutting screw extractor bits can then be used, but again, in our experience, they are often unable to generate enough torque for screw removal in small soft compression screws that are invariably used in forefoot surgery and can result in further damage to the screw head.

At this stage, we recommend saw transection of the screw in line with the planned osteotomy using a standard sagittal saw. The osteotomy cut is marked out in the desired position with a marker pen. The location of the retained screw is noted (figures 1 and 2) to confirm sufficient bone stock to accept new variable pitch compression screws. We use a standard Stryker TPS sagittal saw and 10 mm saw blade to perform the osteotomy, including cutting through the original screws. We found that we were able to saw through the retained screw without undue difficulty. We used two saw blades to complete the osteotomy, due to blunting of the first against the screw. The total time taken to complete the osteotomy and saw through the retained screw was less than 3 min. We used 0.9% saline irrigation throughout for cooling and for metal debris removal, of which there was not an excessive amount (figures 3 and 4). We were able to perform the metatarsal shift without difficulty and had the required space for new distal variable pitch compression screws (figures 5 and 6).

Figure 1.

AP radiographs demonstrating prerevision appearance of foot and position of metal work. AP, anterior–posterior.

Figure 2.

LAT radiographs demonstrating prerevision appearance of foot and position of metal work. LAT, lateral.

Figure 3.

AP clinical photograph showing the revision scarf osteotomy and the original compression screw which has been cut with a sagittal saw.

Figure 4.

LAT clinical photograph showing the revision scarf osteotomy and the original compression screw which has been cut with a sagittal saw.

Figure 5.

AP radiographs demonstrating postrevision correction, new screw as well as original screw position.

Figure 6.

LAT radiographs demonstrating postrevision correction, new screw as well as original screw position. LAT, lateral.

Outcome and follow-up

Both patients were satisfied with the outcome of their revision surgery at 6-month follow-up, with good function and the wounds and osteotomy healing without any complications.

Discussion

It is often assumed that cutting through metal work is difficult and requires specialist tools such as tungsten carbide drills or diamond tipped saws. Using a standard pen drive, sagittal saw blade to cut through retained compression screws may therefore not be considered as an option.

Removal of the variable pitch screws can be a challenge because, due to the softness of the metal, the heads can become damaged easily. This will then leave the surgeon with several known techniques for removing a stripped screw. These include overdrilling with a corer or using a reverse cutting screw extractor to gain purchase into the screw. Screw extractors can cause further damage as the torque required to turn the screws often exceeds that required to damage the screw head. Overdrilling will result in excessive bone loss especially in foot surgery when the bone stock may already be limited. Figures 7 and 8 illustrate the limited bone stock available, as well as the cut and shift lines of a first metatarsal osteotomy.

Figure 7.

LAT illustrations of the cut and shift lines of a scarf osteotomy (illustrated by Ignatius Liew). LAT, lateral.

Figure 8.

AP illustration of the cut and shift lines of a scarf osteotomy (illustrated by Ignatius Liew). AP, anterior–posterior.

One other option is to perform the revision osteotomy proximally to the retained screw(s); however, that may require alternative implants for fixation that would have required preplanning.

A literature search for broken/stripped screw removal techniques in scarf osteotomy did not reveal any findings. Described methods for orthopaedic hardware removal in general suggest the use of a high speed diamond tipped burr² or screw thread suture foil interposition.³

Through our two cases, a 71-year-old man and a 65-year-old woman, we demonstrated that using a standard Stryker TPS pen saw and saw blade, we were able to effectively, safely and with relative ease, cut through the variable pitch compression screws. Both patients underwent revision for recurrence of their hallux valgus deformity at 2 years and 1 year, respectively, post their index procedures. This technique is a useful alternative to the more elaborate techniques that may result in further damage to the host bone stock. Awareness of this technique may help foot and ankle surgeons overcome a significant hurdle with relative ease during revision surgery.

The variable pitch compression screws used in first metatarsal osteotomy are commonly 3.0 mm in diameter manufactured from titanium alloys such as Ti-6Al-4V to American Society for Testing and Materials (ASTM) standards. Pen drive saw blades are typically made from surgical grade stainless steel alloys such as 420 Stainless Steel, Sandvick 7C27Mo2 and UHB716 Stainless Steel.

Hardness of a material is defined as its resistance to deformation, indentation or penetration. Hardness can be measured on the Rockwell hardness scale and is denoted by a HRC number, where a higher number is a harder material. HRC for Ti-6Al-4V is 30–34 and HRC for 420 stainless steel is 45–54. It follows that when two materials of differing hardness come into contact through abrasion, impact or drilling, the softer material will deform more readily, as we have demonstrated in this clinical example.

We do recommend that initial careful exposure of the screw head and an attempt at removal in the standard manner is the primary goal. However, if this fails, then this method of saw transection of retained compression screws has become our preferred technique, and we now routinely prewarn patients prior to revision forefoot surgery.

Learning points.

• This technique is a potential solution for a common problem using readily available instruments.

• This technique to remove stripped screws such as used in scarf osteotomy has not been published before.

• This technique is safe and effective.

• Technique is relevant and applicable to the everyday practice of the foot and ankle community.