Fusion of the first metatarsophalangeal (MTP1) joint is a common surgery performed to correct hallux rigidus, hallux rigidus et valgus and other painful degenerative diseases of the MTP1.

To assess outcomes of our surgical technique including non-union rates, accuracy and aims of correction.

Between September 2011 and November 2020 a total 72 of MTP1 fusions were performed using a low profile, pre-contoured dorsal locking plate and a plantar compression screw. Union and revision rates were analyzed with a minimum clinical and radiological follow up of at least 3 mo (range 3-18 mo). The following parameters were evaluated on pre- and postoperative conventional radiographs: Intermetatarsal angle, Hallux-valgus angle, dorsal extension of the proximal phalanx (P1) in relation to the floor and the angle between the Metatarsal 1 and the P1 (MT1-P1 angle). Descriptive statistical analysis was performed. Pearson analysis was used to assess for correlations between radiographic parameters and achievement of fusion.

An overall union rate of 98.6% (71/72) was achieved. Two out of 72 patients did not primarily fuse with one patient suffering from a non-union, whilst the other demonstrating a radiological delayed union without clinical symptoms, with eventually complete fusion after 18 mo. There was no correlation between the measured radiographic parameters and the achievement of fusion. We believe the reason for the non-union was mainly attributed to the patient’s incompliance without wearing the therapeutic shoe leading to a fracture of the P1. Furthermore, we didn`t find any correlation between fusion and the degree of correction.

With our surgical technique, high union rates (98%) can be achieved using a compression screw and a dorsal variable-angle locking plate to treat degenerative diseases of the MTP1.

Arthrodesis of the metatarsophalangeal (MTP1) joint is a common surgery performed to correct hallux rigidus, hallux rigidus et valgus and other painful degenerative diseases of the MTP1. Furthermore, it is a salvage procedure for failed hallux valgus surgery. High patient satisfaction and union rates have been reported in the literature with union rates ranging from 77% to 100%[1-4]. Nevertheless, nonunion of the arthrodesis has been purported as a common complication with unsatisfying results often leading to revision surgery[5,6].

A wide range of fixation methods has been published showing that biomechanically the most stable construct is a combination of a compression screw and a dorsal locking plate[2,7,8]. Commonly a dorsal plate fixation is used as it offers superior strength and sagittal plane rigidity allowing for immediate weight bearing[9,10]. In our own institution we have been using the combination of a compression screw with a dorsal locking plate for more than 10 years. The technique is similar to the technique published by Kumar et al[11] with slight variations.

The given literature about radiologic outcomes after arthrodesis of the first ray is limited. Therefore, the aim of this study was to retrospectively assess our own patient collective regarding non-union rate, degree of correction, complications, look for independent risk factors of failure and describe our own surgical technique using a compression screw and a dorsal plate while giving some insightful tips on how to avoid classical pitfalls.

This retrospective study was approved by the ethics commission board of northwest- and central-Switzerland and was conducted entirely at the authors institution: BASEC Nr 2021-00837. Patients recruited have provided written informed consent.

Radiographic assessment

The following parameters were evaluated on pre- and postoperative conventional radiographs which are widely used and accepted as the standard of care and decision making[14]: Intermetatarsal angle (IMA), Hallux-valgus angle (HVA), dorsal extension of the P1 in relation to the floor and the angle between the Metatarsal 1 and the P1 (MT1-P1 angle) as shown in Figure 1. Measurements were always taken from recordings of the last available follow-up. All conventional radiographs were recorded during weight bearing. Imaging was analyzed in a blinded manner by two independent orthopedic surgeons on the picture archiving and communication system (PACS) using PACS measurement tools. Fusion was defined as patients being pain free at 3 mo and by vanishing of the gap within the arthrodesis in at least three cortices.

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Figure 1 The radiographic measurements: α = intermetatarsal angle, β = Hallux-valgus angle, γ = P1-Floor, δ = Mt1-P1 angle. A: The radiographic measurements of the intermetatarsal angle; B: The radiographic measurements of the Hallux-valgus angle; C: The radiographic measurements of P1-Floor angle; D: The radiographic measurements of the Mt1-P1 angle.

IMA: The IMA was measured using the long axis of the first and second Metatarsal. An angle of less than 9° was viewed as normal[15].

HVA: The HVA was assessed by using the long axis of the first Metatarsal in relation to the P1. A value of less than 15 was deemed physiologic[16].

Dorsal extension of P1 in relation to the floor: The Angle between the long axis of the P1 in relation to the floor was measured on lateral radiograph to assess the position of the arthrodesis.

Angle between the first MT1 and the P1 angle: The position of the P1 in relation to the MT1 was measured on a lateral standing weight bearing radiograph.

Of 71 patients with 72 feet were included in the study with a minimum follow up of three months. There were 9 male and 62 female patients with an average age of 70.1 years (range 32-90). The body mass index averaged 26.5 kg/m² (range 17-38). Further patient characteristics are displayed in Table 1. Out of these, 71 patients showed a fused arthrodesis (98.6%) at the latest follow-up with one patient suffering from malunion. One patient finally fused after 18 mo showing a delayed union while being asymptomatic throughout the whole period. One patient did not stick to the postop rehab protocol due to a rapidly increasing dementia leading to a P1 fracture. In consideration of the patient's underlying disease and freedom from symptoms, revision surgery was not performed. In one case the locking mechanism of the locking screws failed leading to relapse in valgus and pronation of the first toe which eventually fused in that position. In total three patients developed a symptomatic adjacent joint degeneration over time (15-37 mo). In one case the first tarsometatarsal joint (TMT I) and in two cases the interphalangeal (IP) joint was affected all requiring a TMT or IP joint arthrodesis over time. The preoperative HVA was in average 25.2 (range 14-64) with a correction down to 12 in average (range 2-27) while the preoperative IMA was 13.48 (range 4.5-24) with a postoperative correction to 9.2 in average (range 3.5-15). The preoperative MT1-P1 angle was 8.7 (range -28.05 to 55) with postoperative values of in average 16.89 (-4.05 to 34.5) which was already shown. All radiographic parameters are in detail displayed in Table 2. All patients with diabetes and smoking fused without showing signs of delayed healing or wound healing disorders. Only one patient developed a postoperative wound infection, which ultimately required a skin graft. Preoperatively the patient had a duplex ultrasound which did not show diminished perfusion. During the wound healing disorder another angiography was performed which showed a long-distance stenosis of the superficial femoral artery and the popliteal artery which was treated by balloon dilatation. Another wound healing disorder appeared that was successfully treated with oral antibiotics

Arthrodesis of the MTP1 is a highly successful surgery to treat degenerative diseases of the MTP1. It has already been shown that using a construct of a compression screw and dorsal locking plate offers biomechanically the most stable construct[10]. In our own cohort, union rate was 98.6% (CI: 90.3-99.6) with one nonunion and one delayed union which we counted as a union as it finally fused. One malunion appeared due to failure of the locking mechanism. This patient had a known osteoporosis and suffered over the course of time of insufficiency fractures of the ipsilateral second and third metatarsal as a sign of lowered bone density. The clear nonunion was most likely attributed to a rapidly progressing dementia with incompliance regarding the postop protocol. In a big systemic review with 2656 joint included Roukis found an overall nonunion incidence of 5.4% with a symptomatic nonunion in only 1.8% which is consistent with our own data[17]. Interestingly in our own data, there was no association of nonunion or wound healing disorders with diabetes or smoking[18]. All patients with a nonunion or delayed union were non-diabetic and did not smoke. We used the P1-floor angle to radiologically assess the sagittal position of the great toe as already described[1,19]. A valgus of 5-20 degrees in the ap view has been recommended as a desired result in an earlier publication[16]. In our own cohort we measured an average postoperative valgus of 12 (range 2-27) which is again, consistent with recently published data[20]. The postoperative IMA was 9.2 (3.5-15) which can be deemed as borderline if you apply the cut-off values as mentioned above. Correspondingly McKean et al[21] showed that a complete correction of the IMA cannot be achieved in patients undergoing MTP1 fusion for severe HV deformity without an additional first metatarsal osteotomy[21]. We didn`t find any correlation between the amount of correction and risk of nonunion which is most likely attributed to the small numbers as according to Weber et al[18] negative influencing factors were the presence of preexisting diseases, higher grades of osteoarthritis, and a relative increased dorsiflexion position of the great toe after surgery[18].

The MT1-P1 angle was used to assess the sagittal position of the first ray. In our opinion this needs to be done intraoperatively using a flat tray as mentioned above and recommended by Drittenbass et al[20] simulating a weight-bearing situation as the MT1-P1 is strongly influenced by the position of the first metatarsal which differs in flatfoot, cavo-varus or other foot deformities reflected by the wide postoperative range and has to be taken into account intraoperatively[20]. Accordingly, we observed a wide range of the MT1-P1 angle in our own cohort with an average value of 16.89 (-4.05 to 34.5). This has already been published long ago deeming an average value of 12 degrees (range 0-32) as physiologic[22,23].

Strengths of the present study are more certainly that a SB performed all surgeries, and the same implant and fixation technique were used in all cases. Limitations of this study include the short period of follow up and the lack of clinical scores to correlate radiological and clinical outcome. Future studies should particularly correlate radiological data with clinical scores to confirm their clinical relevance and superiority.

We were able to show that with our surgical technique, high union rates (98%) can be achieved using a compression screw and a dorsal variable-angle locking plate to treat degenerative diseases of the MTP1 even in diabetic and smoking patients.