The January transfer window is generally seen as a way of reinforcing squads rather than really rejuvenating them.

After the hard-fought festive games it is a chance to add bodies to your team ahead of the final charge. Occasionally it provides much more, as teams find a real hero during the winter window. Here we look at five of the SPL players that really made an impact when they moved on deadline day of the January transfer period.

Steven Davis – Fulham to Rangers (loan)

The winter loan deal is often a way of patching up an ailing squad with players surplus to requirements, or offering experience to a highly regarded youngster from a club south of the border. Steven Davis arrived at Ibrox on loan and set about becoming arguably the single most important player at the club in recent years.

Walter Smith took a 23-year-old Davis to Ibrox from Fulham, where he had suffered from being part of Lawrie Sanchez’s failed attempts to turn the West London side into Northern Ireland. The midfielder was thrust into the thick of the action, making his debut against Panathinaikos and scoring his first goal against Werder Bremen. He helped the club to the cup double as well as the Europa League final in his first season.

A fee of around £3 million was enough to make the move permanent and Davis grew in stature with every passing season. He scored six and set up seven in his first full season, recording another four goals and 14 assists in 2009/10. This season he already has ten assists and three goals to his name.

Robbie Keane – Tottenham to Celtic (loan)

A great transfer not only adds to the quality of the team, but excites the supporters, prompting increased shirt sales and more people through the turnstiles. In the winter window, most deals tend to be functional, rather than fun.

Robbie Keane was both, arriving from Spurs on a six-month loan deal. The Irishman scored 16 goals in 19 games in all competitions and proved such a fan favourite that he’ll be perennially linked with a return to Celtic Park until the day he retires. It won’t be this window, as he’s on loan at Aston Villa from LA Galaxy, but one day…

Chris Maguire – Aberdeen to Kilmarnock (loan)

Although not an immediately obvious inclusion, the fact that Kilmarnock remain in the SPL tells you all you need to know about Maguire’s contribution to Killie at the end of 2009/10.

Rooted to the bottom of the table at the end of January, and with a record of one win in 13 matches, Kilmarnock seemed doomed to relegation. The arrival of Jimmy Calderwood on a firefighting mission was something of a turning point. Calderwood took Maguire on a deadline day loan from his former club, Aberdeen, and set about saving Kilmarnock from the drop.

The forward scored the only goal of the game in a 1-0 win over Celtic. A week later he set up Craig Bryson for the only goal of the game against Falkirk. Three days later? A goal and an assist in a 3-2 win against St Johnstone. Between his arrival and the end of the season Kilmarnock scored a paltry nine goals. Maguire scored four of them and assisted in a further two as Killie survived by a single point.

Barry Robson (Dundee United to Celtic)

Dundee United had done a shrewd piece of business when they acquired Barry Robson from Inverness for a five figure sum. The talented midfielder would go on to produce a strike-rate of a goal every five games from the centre of the park. He would also make his full Scotland debut as a second half substitute for Gary Caldwell in the 1-0 friendly victory over South Africa while still at Tannadice.

On deadline day 2008 Dundee United accepted an offer of over £1 million and Robson moved to Glasgow. He scored on his debut against Aberdeen and ten days later put Celtic 2-1 up on Barcelona in the Champions League. Arguably most importantly of all, it was Robson who scored the winning goal to give Celtic a 3-2 victory over Rangers in April 2008. Robson moved to Middlesbrough in January 2010.

Ryan Stevenson (Ayr United to Hearts)

Hearts were taking a long shot on 25-year-old midfielder Ryan Stevenson when they brought him in on the last day of January 2010 from Ayr United. Rejected by Chelsea as a youngster, the creative midfielder had fallen out of favour at St Johnstone before his move to Ayrshire. Several SPL clubs had taken a look at Stevenson following some fine performances for the Honest Men, but it was Hearts that made the move first.

Stevenson became a firm fixture in the Hearts team and finished the 2010/11 season with seven goals. He was rewarded for his form with a call-up to the Scotland national team for the match against Cyprus in November last year. He moved to Ipswich Town earlier this week.