Joint replacement – Stryker SR MCP cemented joint

Dorsal midline skin incision drawn over outline of MCPJ.
This cemented joint replacement can be performed under a regional or general anaesthetic and takes around an hour to complete.
Once the patient is anaesthetised and supine with their arm on an arm table, an upper arm tourniquet is applied and the limb exsanguinated. The limb is prepped and draped and skin markings are drawn.
A line is drawn along the dorsal central portion of the joint along the proximal phalanx and metacarpal and to show the rough outline of the metacarpal phalangeal joint.
The incision extends from the metacarpal neck to just distal to the web spaces as shown on the picture.
This line can be extended along the metacarpal and phalanx to aid in alignment later in the procedure if wanted.

The skin is incised and tissue elevated to expose the extensor mechanism.

The extensor tendon is then split in the midline along the length of the wound.When incising the tendon care must be taken to keep the joint capsule as a separate layer. If these layers are separated at this point it makes a layered closure easier at the end of the procedure. Occasionally in rheumatoid arthritis patients this is very difficult due to the adherent tissue caused by the synovitis.

The joint capsule is then opened in the midline to expose the joint.

The joint capsule on the proximal phalanx is then elevated.This elevation is around to the volar third of the bone both ulnarly and radially (very similar to a release around the tibia during a total knee replacement).

The release is completed to give a clearer view of the joint. The collateral ligaments are left intact.

A line perpendicular to the diaphysis is drawn across the head of the metacarpal.The line at this level to indicate the head resection ‘cut’ line whilst preserving the collateral ligaments.
The level of the collateral ligaments on the metacarpal head are identified using a Watson-Cheyne dissector. It can also be seen on the diagram that the longitudinal line draw on the skin along the metacarpal shaft is perpendicular to the ‘cut’ line on the metacarpal head. In patients with a distorted metacarpal head this additional skin line can be very useful to orientate the bony cut.

The head is cut distal to the collateral ligaments.The cut is made with a narrow oscillating saw. During all bone resections the collateral ligaments are protected with Hohmann retractors or a Watson-Cheyne dissector.
The slice of head can be seen in the picture, this is removed.

The soft tissues around the base of the proximal phalanx are mobilised.The proximal phalanx is then brought into view. This may require a little more dissection to achieve although is often possible by placing a thumb on the dorsum of the head of the proximal phalanx and using the index finger on the volar base of the phalanx to pull it forward into view.
Do not use a instrument to lean on the cut surface of the metacarpal head and lever the phalanx into place as this can distort the metacarpal on which the prosthesis will sit.

A bone resection of the proximal end of the proximal phalanx is performed perpendicular to the diaphysis.Once adequately exposed, the soft tissues are protected and the base of the proximal phalanx is removed just below the articular cartilage perpendicular to the shaft.
Be aware that the deepest part of the joint surface is the centre and therefore to achieve a thin resection centrally, a much thicker resection peripherally is required. In very eroded joints the central portion may not be resected in this cut and may need to be removed with a burr to allow for reaming.
Also be careful to keep the proximal phalanx vertical and the saw parallel to the table as it is very easy to lift the hand during sawing and resect too much bone from the volar aspect of the phalanx.

The resected piece of the phalanx is shown.

An awl from the joint replacement set is then used to find the diaphysis of the metacarpal.For the metacarpal, the diaphysis is central in the radial to ulnar direction and at the junction between the dorsal third and middle third in the volar to dorsal direction.
When measuring the thirds it is important to count the whole AP dimension of the head not just the cut surface.

The awl is then full inserted and should go easily to its full lenght in the metacarpal. A radiograph can be taken at this point if desired to check position.

The volar part of the articular cartilage now needs to be removed with at 45 degree freehand cut.A line can be drawn at roughly the half way point from dorsal to volar of the head (the whole head not the flat face seen following the initial resection – see manufacturers operative technique for diagramatic representation).

The volar articular surface is then resected along this line at a 45 degree angle to the previous cut. Be careful with depth as the volar plate and flexor tendons are just beyond the end point of the cut.

The volar cut is then removed and it is useful at this point to slide a McDonald retractor over each cut surface to assure they are flat and with no osteophytes of protruberances which will interfere with joint movement or seating of the prosthesis.

The extension joint gap is assessed.Usually the tip of the little finger can be placed in the gap between the bones in full extension. If very tight it is likely that the trial implants will be tight and therefore extension of the finger will be tight or limited.

The awl is then placed centrally in both planes into the proximal phalanx.Occasionally a burr will be required to allow the awl to pass.
A radiograph can be taken to check positioning which needs to be central in the canal of the diaphysis on both PA and lateral views.

Again a skin line along the phalanx can aid central positioning.
Noting the black handles flat surface as parallel to the phalanx bony cut is also useful to review to double check the angle of the bone cut (This technique can also be used for the metacarpal to check bone cut angles when the awl is inserted initially).

The reamers are then used starting with XS in the proximal phalanx.The reamers are labelled clearly as shown with size, bone and dorsal to aid orientation.
When sizing implants always size up the phalanx first as this is the smallest bone EXCEPT in the case of the 4th/Ring finger where the diaphysis of the metacarpal can be very narrow and it is advised to either start with the metacapal reaming to size the implant or ream both bones sequentially working up the sizes to find the best fit.
A radiograph may also be taken at this point and is slightly off centre the next reamers can be reamed eccentrically to centralise the final size.

Radiographs are taken to check placement of the initial reamer in the proximal phalanx.PA view of XS reamer in proximal phalanx – acceptable and central.

This lateral view is a little difficult to see but it reveals the entry point of the reamer to be slightly volar therefore the next sizes were reamed with dorsal pressure to centralise the reamers in the bone.

The XS metacarpal reamer is inserted.

Radiographs are taken to check placement of the initial reamer in the metacarpal.This PA radiograph reveals the reamer to be slightly radial in its placement. Subsequent sizes were therefore reamed with ulnar pressure to centralise the final reamer.

The lateral radiograph with close inspection reveal a good entry point for the reamer in line with the diaphysis however the tip of the reamer is leaning slightly volar which was taken into account when reaming the larger sizes.

An XL reamer is deemed a snug fit and dictates the size of implant chosen.With the proximal phalanx sized the largest reamer often requires the slap-hammer from the implant tray to remove it.

The metacarpal is reamed to the corresponding XL size.NB – It is important to note the rotation of the reamers when reaming and ensure the dorsal flat surface is kept parallel to the dorsum of the finger.

The XL trial implants are then inserted.The trials are tapped into place with the corresponding impactors (which will also be used for the final implant insertion).
For ease the metacarpal implant is usually inserted first and then the phalan implant.
IMPORTANT NOTE – It is worth noting if trial insertion is difficult and the manoeuvre which is then used to smoothly insert the phalanx trial and this will become very important when the final implant is being inserted and the cement is setting!
Once the trial is seated the finger can be put through a range of movement.
Joints should extended fully and have some slight hyperextension with almost no tension. If the finger springs back sharply into flexion then more bone will need to be resected.
Flexion should be smooth, it is usually full even in a previously stiff finger as the dorsal capsule is open. Catching, restriction or clicking in flexion can signify a retained bone fragment, osteophyte or lip on the bone cut. This will need to be identified and resected before the final implants are inserted. An intra-operative radiograph can aid this.

Rotation and range of movement of the trials are assessed.Note the rotation of the trial implants using the grooves on their dorsum which should align with each other, with the centre of the finger and with the skin lines previously drawn.
Note that the trail implants are slightly larger then the final implant which and smaller to allow for a cement mantle.
The trials are removed using a sharp towel clip which grips into the 2 holes on the radial and ulnar sides of each component.

Radiographs are taken to assess trial positioning.PA radiograph show the centrally placed trial implants and a snug fit both in the diaphysis but also in the width of the prosthesis relative to the bone which was excised.

The lateral radiograph shown a good central location.

Prosthesis is checked for size and expiry date and then opened.XL reamers and prosthesis colour coded – RED.

The joint and bones are washed out and tipped up to remove excess fluid.

The bone ends are seen clean, dry and with no tissue obstructing implant insertion.
At this point the surgeon needs to prepare for cementing.
Have the implant open and easily accessible to the surgeon without it needing to be passed by another person.
Have the impactors for the implant and the mallet.
Have tools to remove excess cement – Watson-Cheyne or McDonald’s dissector, clean forceps, a fresh 15 blade.
Change gloves to a clean pair and dip fingertips in saline to ease cement handling.
Recall the manoeuvre used to smoothly seat the proximal phalanx implant.
Once all is ready then cement mixing can begin.

Cement is inserted into both bones.Cementing can be performed with quick setting cement which is usually injected into the bones via a syringe or. as in this case, longer setting cement which is serially impacted with then thumb into the reamed bone when easily handleable.

The metacarpal implant is sited and impacted.

The phalanx hidden beneath the metacarpal portion of the implant will now need to be pulled forward to allow phalangeal implant to be inserted.

The phalangeal implant is sited and impacted and all excess cemented removed.Make sure to remove any excess volar cement which can be hidden.
If a small excess is located on the edge of the implant when the cement is almost set it is better to cut it flush with the implant edge rather than try to pull it away as pulling the cement may bring with it a segment which was sitting underneath the implant and best left in place.

Implant rotation and range of movement assessed.Once the cement is set the range of movement is checked and alignment again seen by the grooves on the dorsum of the implant.

Full extension achieved with almost no force and no tight recoil into flexion.

Tenodesis manoeuvre to show flexion cascade.

Radiographs are taken of the final implant in-situ.PA intra-operative radiograph show the final position of the implant and cement mantle around the ‘plastic’ phalangeal implant.

Lateral intra-operative radiograph.

The joint capsule is closed using an absorbable suture.

The extensor mechanism is repaired with a 4/0 PDS.

The skin is closed with an absorbable continuous suture.

An adherent dressing is used.

A volar plaster slab is applied.

Lateral pre-operative radiographs revealling 3rd MCPJ arthritis.

PA pre-operative radiographs revealling 3rd MCPJ arthritis.

PA post-operative radiographs.
Note the slight rotation of the hand which can be seen by the asymmetrical shape of the remaing 3rd metacarpal head and therefore the rotation of the implant seen be the different amounts the head overhangs the stem (more on the radial side due to slight supination).

Lateral post-operative radiographs.